U.S. patent number 10,032,919 [Application Number 14/756,480] was granted by the patent office on 2018-07-24 for method for manufacturing semiconductor device.
This patent grant is currently assigned to Semiconductor Energy Laboratory Co., Ltd.. The grantee listed for this patent is SEMICONDUCTOR ENERGY LABORATORY CO., LTD.. Invention is credited to Tomoaki Moriwaka.
United States Patent |
10,032,919 |
Moriwaka |
July 24, 2018 |
Method for manufacturing semiconductor device
Abstract
The invention relates to a method for forming a uniform silicide
film using a crystalline semiconductor film in which orientation of
crystal planes is controlled, and a method for manufacturing a thin
film transistor with less variation in electric characteristics,
which is formed over an insulating substrate using the silicide
film. A semiconductor film over which a cap film is formed is
irradiated with a laser to be crystallized under the predetermined
condition, so that a crystalline semiconductor film including large
grain crystals in which orientation of crystal planes is controlled
in one direction is formed. The crystalline semiconductor film is
used for silicide, whereby a uniform silicide film can be
formed.
Inventors: |
Moriwaka; Tomoaki (Kanagawa,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
SEMICONDUCTOR ENERGY LABORATORY CO., LTD. |
Atsugi-shi, Kanagawa-ken |
N/A |
JP |
|
|
Assignee: |
Semiconductor Energy Laboratory
Co., Ltd. (Kanagawa-ken, JP)
|
Family
ID: |
39775152 |
Appl.
No.: |
14/756,480 |
Filed: |
September 9, 2015 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20160005611 A1 |
Jan 7, 2016 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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12076585 |
Mar 20, 2008 |
9177811 |
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Foreign Application Priority Data
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Mar 23, 2007 [JP] |
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2007-077217 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
21/28518 (20130101); H01L 29/41733 (20130101); H01L
27/1285 (20130101); H01L 21/02691 (20130101); H01L
29/78618 (20130101); H01L 21/02609 (20130101); H01L
29/458 (20130101); H01L 21/02683 (20130101); H01L
21/02686 (20130101); H01L 29/78654 (20130101); H01L
29/045 (20130101); H01L 21/02592 (20130101); H01L
21/02532 (20130101) |
Current International
Class: |
H01L
21/84 (20060101); H01L 29/45 (20060101); H01L
29/786 (20060101); H01L 21/02 (20060101); H01L
21/285 (20060101); H01L 29/04 (20060101); H01L
29/417 (20060101); H01L 27/12 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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61-185917 |
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Aug 1986 |
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JP |
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62-165908 |
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Jul 1987 |
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JP |
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63-299322 |
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Dec 1988 |
|
JP |
|
07-135324 |
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May 1995 |
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JP |
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2000-228360 |
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Aug 2000 |
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JP |
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2001-338894 |
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Dec 2001 |
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JP |
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2003-218362 |
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Jul 2003 |
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JP |
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2004-048029 |
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Feb 2004 |
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JP |
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2004-165436 |
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Jun 2004 |
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JP |
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2005-117029 |
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Apr 2005 |
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JP |
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2005-217209 |
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Aug 2005 |
|
JP |
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2005-277062 |
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Oct 2005 |
|
JP |
|
2008-252076 |
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Oct 2008 |
|
JP |
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Other References
Akito Hara, Fumiyo Takeuchi, Michiko Takei, Katsuyuki Suga, Kenichi
Yoshino, Mitsuru Chida, Yasuyuki Sano and Nobuo Sasaki,
High-Performance Polycrystalline Silicon Thin Film Transistors on
Non-Alkali Glass Produced Using Continuous Wave Laser Lateral
Crystallization, Japanese Journal of Applied Physics, vol. 41, Part
2, No. 3B, 2002. cited by examiner .
Hara.A et al., "Ultra-High Performance Poly-Si TFTs on a Glass by a
Stable Scanning CW Laser Lateral Crystallization", AM-LCD '01
Digest of Technical Papers, 2001, pp. 227-230. cited by applicant
.
Office Action for U.S. Appl. No. 14/756,870 dated Sep. 8, 2016.
cited by applicant.
|
Primary Examiner: Tornow; Mark
Attorney, Agent or Firm: Nixon Peabody LLP Costellia;
Jeffrey L.
Claims
What is claimed is:
1. A method of manufacturing a semiconductor device comprising:
forming a semiconductor film comprising amorphous silicon over a
substrate; forming a cap film over the semiconductor film, wherein
the cap film comprises SiNxOy (x<y) and has a thickness of
greater than or equal to 200 nm; emitting a first laser beam having
a length along a first direction and a width along a second
direction, the first laser beam including TEM.sub.00 mode; shaping
the first laser beam to a second laser beam having a linear shape,
wherein the step of shaping includes: modifying the first laser
beam along the first direction by using a first cylindrical lens;
and modifying the first laser beam along the second direction by
using a second cylindrical lens, irradiating the semiconductor film
with the second laser beam through the cap film to crystallize the
semiconductor film; forming a metal film in contact with a portion
of the semiconductor film after the semiconductor film is
irradiated with the second laser beam; and forming a silicide film
by a reaction between the metal film and the semiconductor film,
wherein the semiconductor film comprises a crystal region of which
crystal plane orientation in a direction perpendicular to a surface
of the semiconductor film is {001}.
2. The method according to claim 1, wherein the crystal region
occupies 40% or more of the semiconductor film.
3. The method according to claim 1, wherein the semiconductor film
has a thickness of greater than or equal to 10 nm and less than or
equal to 100 nm.
4. The method according to claim 1, wherein the semiconductor film
is formed on an insulating film having a thickness of 50 to 150
nm.
5. The method according to claim 1, wherein the first laser beam is
emitted from a CW laser or a pseudo CW laser.
6. The method according to claim 1, wherein the cap film has an
etching rate of greater than or equal to 1 nm/min and less than or
equal to 150 nm/min with respect to a mixture solution containing
ammonium hydrogen fluoride and ammonium fluoride at 20.degree.
C.
7. A method of manufacturing a semiconductor device comprising:
forming a semiconductor film comprising amorphous silicon over a
substrate; forming a cap film over the semiconductor film, wherein
the cap film comprises SiNxOy (x<y) and has a thickness of
greater than or equal to 200 nm; emitting a first laser beam having
a length along a first direction and a width along a second
direction, the first laser beam including TEM.sub.00 mode; shaping
the first laser beam to a second laser beam having a linear shape,
wherein the step of shaping includes: modifying the first laser
beam along the first direction by using a first cylindrical lens;
and modifying the first laser beam along the second direction by
using a second cylindrical lens, irradiating the semiconductor film
with the second laser beam through the cap film to crystallize the
semiconductor film; etching the crystallized semiconductor film to
form a semiconductor island; forming a gate insulating film over
the semiconductor island; forming a gate electrode over the
semiconductor island; forming a source region and a drain region in
the semiconductor island; forming an insulating film over the gate
electrode to cover the semiconductor island; forming a metal film
over the insulating film and in contact with the source region and
the drain region; and forming silicide films on the source region
and the drain region by heating.
8. The method according to claim 7, wherein the semiconductor film
has a thickness of greater than or equal to 10 nm and less than or
equal to 100 nm.
9. The method according to claim 7, wherein the semiconductor film
is formed on an insulating film having a thickness of 50 to 150
nm.
10. The method according to claim 7, wherein the first laser beam
is emitted from a CW laser or a pseudo CW laser.
11. The method according to claim 7, wherein the cap film has an
etching rate of greater than or equal to 1 nm/min and less than or
equal to 150 nm/min with respect to a mixture solution containing
ammonium hydrogen fluoride and ammonium fluoride at 20.degree.
C.
12. A method of manufacturing a semiconductor device comprising:
forming a semiconductor film comprising amorphous silicon over a
substrate; forming a cap film over the semiconductor film, wherein
the cap film comprises SiNxOy (x<y) and has a thickness of
greater than or equal to 200 nm; emitting a first laser beam having
a length along a first direction and a width along a second
direction, the first laser beam including TEM.sub.00 mode; shaping
the first laser beam to a second laser beam having a linear shape,
wherein the step of shaping includes: modifying the first laser
beam along the first direction by using a first cylindrical lens;
and modifying the first laser beam along the second direction by
using a second cylindrical lens, irradiating the semiconductor film
with the second laser beam through the cap film to crystallize the
semiconductor film; etching the crystallized semiconductor film to
form a semiconductor island; forming a gate insulating film over
the semiconductor island; forming a gate electrode over the
semiconductor island; forming a source region and a drain region in
the semiconductor island; forming an insulating film over the gate
electrode to cover the semiconductor island; hydrogenating the
semiconductor island by heating after forming the insulating film;
forming a metal film over the insulating film and in contact with
the source region and the drain region; and forming silicide films
on the source region and the drain region by heating.
13. The method according to claim 12, wherein the semiconductor
film has a thickness of greater than or equal to 10 nm and less
than or equal to 100 nm.
14. The method according to claim 12, wherein the semiconductor
film is formed on an insulating film having a thickness of 50 to
150 nm.
15. The method according to claim 12, wherein the first laser beam
is emitted from a CW laser or a pseudo CW laser.
16. The method according to claim 12, wherein the insulating film
comprises silicon nitride.
17. The method according to claim 12, wherein the step of
hydrogenating the semiconductor island is performed by heating in
an atmosphere containing hydrogen.
18. The method according to claim 12, wherein the cap film has an
etching rate of greater than or equal to 1 nm/min and less than or
equal to 150 nm/min with respect to a mixture solution containing
ammonium hydrogen fluoride and ammonium fluoride at 20.degree.
C.
19. A method of manufacturing a semiconductor device comprising:
forming a semiconductor film comprising amorphous silicon over a
substrate; forming a cap film over the semiconductor film, wherein
the cap film comprises SiNxOy (x<y) and has a thickness of
greater than or equal to 200 nm; emitting a first laser beam having
a length along a first direction and a width along a second
direction; shaping the first laser beam to a second laser beam
having a linear shape, wherein the step of shaping includes:
modifying the first laser beam along the first direction by using a
first cylindrical lens; and modifying the first laser beam along
the second direction by using a second cylindrical lens,
irradiating the semiconductor film with the second laser beam
through the cap film to crystallize the semiconductor film; forming
a gate insulating film over the semiconductor film after the
semiconductor film is irradiated with the second laser beam;
forming a gate electrode over the gate insulating film; forming an
insulating film over the gate electrode to cover the semiconductor
film; forming a metal film over the insulating film and in contact
with a portion of the semiconductor film; and forming a silicide
film by a reaction between the metal film and the semiconductor
film, wherein the semiconductor film comprises a crystal region of
which crystal plane orientation in a direction perpendicular to a
surface of the semiconductor film is {001}.
20. The method according to claim 19, wherein the semiconductor
film has a thickness of greater than or equal to 10 nm and less
than or equal to 100 nm.
21. The method according to claim 19, wherein the semiconductor
film is formed on an insulating film having a thickness of 50 to
150 nm.
22. The method according to claim 19, wherein the first laser beam
is emitted from a CW laser or a pseudo CW laser.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing a
semiconductor device with high characteristics. Note that a
semiconductor device in the present specification generally
indicates a device capable of functioning by utilizing
semiconductor characteristics, and electro-optic devices,
semiconductor circuits, and electronic devices are all
semiconductor devices.
2. Description of the Related Art
In accordance with reduction in size of an integrated circuit, a
semiconductor device which forms the integrated circuit is required
to have lower contact resistance between a metal wiring and a
semiconductor film and lower resistance of an impurity region in
the semiconductor film. Therefore, a technique in which contact
resistance and resistance of an impurity region are reduced by
forming a silicide film on the semiconductor film has been adopted
in a semiconductor field. When resistance of a semiconductor film
is reduced, ON current of a semiconductor device is improved and a
semiconductor device with high characteristics can be
manufactured.
The silicide film is usually formed as follows: a CW
(continuous-wave) laser or a pulsed laser with high repetition rate
of 10 MHz or more (pseudo CW laser) is formed into a beam spot; an
amorphous semiconductor film is irradiated with the laser; a
solid-liquid interface to be formed by laser irradiation is moved
to generate lateral crystal growth, so that a crystalline
semiconductor film is formed; a metal film is formed thereover; and
heat treatment is performed to react the crystalline semiconductor
film and the metal film, whereby a silicide film is formed in the
interface therebetween (for example, Reference 1: Japanese
Published Patent Application No. H7-135324).
The crystalline semiconductor film obtained by the lateral crystal
growth has characteristics that the crystals each have a large
grain size and orientation of crystal planes in adjacent crystals
with a large grain size is entirely different. The orientation of
crystal planes in each crystal with a large grain size
(hereinafter, referred to as large grain crystal) formed in a
region irradiated with a laser beam is random; therefore,
orientation of crystal planes in large grain crystals cannot be
controlled in one direction.
Composition and a grow rate of the silicide to be formed is
determined depending on the relation of surface energy between the
semiconductor film and the silicide film to be formed. Accordingly,
the silicide reaction between the metal film and the above
crystalline semiconductor film in which the orientation of crystal
planes in adjacent large grain crystals is random reflects random
orientation of crystal planes in the semiconductor film. Thus,
there is a problem in that composition and a thickness of silicide
to be formed are not uniform.
SUMMARY OF THE INVENTION
In view of the foregoing problem, it is an object of the present
invention to form a uniform silicide film using a crystalline
semiconductor film in which orientation of crystal planes is
controlled and to realize miniaturization and high performance of a
field effect transistor which has little variation of electric
characteristics formed over an insulating substrate.
When a large amount of heat is supplied to the semiconductor film
at one time, the semiconductor film is completely melted, and a
large quantity of crystal nuclei is generated in the semiconductor
film. Then, disordered crystal growth is cased by these crystal
nuclei. This is a reason of random orientation in crystal planes of
crystals that are laterally grown with the use of a CW laser or a
pseudo CW laser.
It has been considered by the inventor of the present invention
that suppression of disordered crystal growth is important to
control the orientation of crystal planes. As a result of research,
it has been found that a cap film is formed over an amorphous
semiconductor film that is formed over an insulating substrate such
as a glass substrate, and irradiation with a laser beam for lateral
crystal growth by laser crystallization is performed under the
predetermined conditions, whereby a crystalline semiconductor film
including large grain crystals in which orientation of crystal
planes is controlled in one direction can be formed. When a metal
film is formed over the above-described crystalline semiconductor
film in which orientation of crystal planes is controlled in one
direction, and a silicide film is formed by heat treatment,
silicide reaction between the semiconductor film and the metal film
proceeds without influence of dependency on orientation of crystal
planes; therefore, a silicide film with extremely uniform in the
film plane can be formed.
Note that silicide in this specification indicates general
compounds of semiconductor and metal as well as a compound of
silicon and a metal.
By irradiating the semiconductor film over which the cap film is
formed with a laser to be crystallized under the predetermined
conditions, a crystalline semiconductor film including large grain
crystals in which orientation of crystal planes is controlled in
one direction can be obtained. When the crystalline semiconductor
film is used for silicide, random silicide reaction that is
dependent on orientation of crystal planes can be suppressed;
therefore, a uniform silicide film can be formed. Accordingly, a
semiconductor device with little variation can be manufactured. As
a result, miniaturization and high performance of a filed effect
transistor can be realized.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A to 1D are diagrams illustrating a method for manufacturing
a semiconductor device in Embodiment Mode 1 of the present
invention.
FIGS. 2A to 2C are diagrams illustrating a method for manufacturing
a semiconductor device in Embodiment Mode 1 of the present
invention.
FIG. 3 is a diagram showing an optical device used for manufacture
of a crystalline semiconductor film in Embodiment Mode 2 of the
present invention.
FIG. 4 is a diagram showing conditions of a laser beam and
orientation of crystal planes in Embodiment Mode 2 of the present
invention.
FIGS. 5A to 5F are diagrams each showing an observation result of a
sample in Embodiment Mode 2 of the present invention.
FIGS. 6A to 6F are diagrams each showing an observation result of a
sample in Embodiment Mode 2 of the present invention.
FIGS. 7A to 7F are diagrams each showing an observation result of a
sample in Embodiment Mode 2 of the present invention.
FIG. 8 is a diagram showing an optical device used for manufacture
of a crystalline semiconductor film in Embodiment Mode 3 of the
present invention.
FIGS. 9A and 9B are diagrams showing energy distribution of a laser
beam used for manufacture of a crystalline semiconductor film in
Embodiment Mode 3 of the present invention.
FIGS. 10A to 10F are diagrams showing an observation result of a
sample in Embodiment Mode 3 of the present invention.
FIGS. 11A to 11D are cross-sectional views illustrating a
manufacturing step of an active matrix substrate in Embodiment 1 of
the present invention.
FIGS. 12A to 12C are cross-sectional views illustrating a
manufacturing step of an active matrix substrate in Embodiment 1 of
the present invention.
FIGS. 13A to 13C are cross-sectional views illustrating a
manufacturing step of an active matrix substrate in Embodiment 1 of
the present invention.
FIGS. 14A to 14C are cross-sectional views each illustrating a step
of manufacturing an active matrix substrate in Embodiment 1 of the
present invention.
FIG. 15 is a top view of a pixel portion of an active matrix
substrate in Embodiment 1 of the present invention.
FIG. 16 is a cross-sectional view illustrating a manufacturing step
of an active-matrix liquid crystal display device in Embodiment 2
of the present invention
FIG. 17 is a cross-sectional view of a structure of a driver
circuit and a pixel portion of a light-emitting device in
Embodiment 3 of the present invention.
FIG. 18A is a top view showing a driver circuit and a pixel portion
of a light-emitting device in Embodiment 3 of the present
invention, and FIG. 18B is a cross-sectional view thereof.
FIGS. 19A to 19E are diagrams each showing an example of a
semiconductor device in Embodiment 3 of the present invention.
FIGS. 20A to 20C are diagrams each showing an example of a
semiconductor device in Embodiment 4 of the present invention.
FIGS. 21A to 21D are diagrams each showing an example of a
semiconductor device in Embodiment 5 of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Embodiment modes of the present invention will be described with
reference to the accompanying drawings. Note that the present
invention can be implemented in various modes, and it is easily
understood by those skilled in the art that modes and details can
be modified in various ways without departing from the purpose and
the scope of the present invention. Accordingly, the present
invention should not be interpreted as being limited to the
description of the embodiment modes below. Note that like portions
in the drawings may be denoted by the like reference numerals, and
repetition explanation thereof is omitted.
Embodiment Mode 1
In this embodiment mode, a cap film is formed over an amorphous
semiconductor film, and the amorphous semiconductor film is
irradiated with a continuous wave laser beam or a pulsed laser beam
with repetition rate of 10 MHz or more under the predetermined
conditions through the cap film, so that a crystalline
semiconductor film in which crystal planes in a perpendicular
direction to a surface are orientated along {001} is formed. Then,
an example in which silicide films are formed in a top gate TFT in
which the crystalline semiconductor film is used for a source
region and a drain region is described. FIGS. 1A to 2C are diagrams
illustrating manufacturing steps thereof.
In FIGS. 1A to 1D, an insulating film 101 functioning as a base
film is formed on one of insulating surfaces of a substrate 100.
The insulating film 101 functioning as a base film is formed using
a silicon oxide film, a silicon nitride film, a silicon nitride
oxide film containing a larger amount of nitrogen than that of
oxygen, a silicon oxynitride film containing a larger amount of
oxygen than that of nitrogen, each of which has a thickness of 50
to 150 nm, or the like as appropriate. Here, as the substrate 100
having an insulating surface, a glass substrate with a thickness of
0.7 mm is, for example, used. Further, as the insulating film 101
functioning as a base film, a silicon nitride oxide film with a
thickness of 50 nm and a silicon oxynitride film with a thickness
of 100 nm are formed by a plasma CVD method.
Next, an amorphous silicon film with a thickness of greater than or
equal to 10 nm and less than or equal to 100 nm, preferably,
greater than or equal to 20 nm and less than or equal to 80 nm, is
formed as a semiconductor film 102 over the insulating film 101 by
a plasma CVD method.
In the case where the semiconductor film 102 is an amorphous
silicon film, after formation of the semiconductor film 102, the
semiconductor film 102 may be heated. The heat treatment is for
extracting hydrogen from the amorphous silicon film. Note that
hydrogen is extracted so as to prevent a hydrogen gas from jetting
from the semiconductor film 102 when irradiation with a laser beam,
and the heat treatment can be omitted if the amount of hydrogen
contained in the semiconductor film 102 is small. Here, the
semiconductor film 102 is heated in an electric furnace at
500.degree. C. for 1 hour.
Next, a SiN.sub.xO.sub.y film (0.ltoreq.x.ltoreq.4/3,
0.ltoreq.y.ltoreq.2, 0.ltoreq.3x+2y.gtoreq.4) with a thickness of
greater than or equal to 200 nm and less than or equal to 1000 nm
is formed as a cap film 103 over the semiconductor film 102. It is
particularly to be noted that if the cap film 103 is too thin, it
will become difficult to control orientation of crystal planes in a
crystalline semiconductor film that is formed later; therefore, the
cap film 103 is preferably formed with a thickness of greater than
or equal to 200 nm and less than or equal to 1000 nm.
The cap film 103 can be formed using a silicon oxide film, a
silicon nitride film, a silicon oxynitride (hereinafter, refer to
as SiO.sub.xN.sub.y (x<y)) film containing a larger amount of
oxygen than that of, nitrogen, a silicon nitride oxide
(hereinafter, refer to SiN.sub.xO.sub.y (x>y)) film containing a
larger amount of nitrogen than that of oxide, or the like. In a
case where a large amount of hydrogen is contained in the cap film
103, heat treatment for extracting hydrogen is performed similarly
to the case of the semiconductor film 102.
As the cap film 103, a film having enough transmittance with
respect to a wavelength of the laser beam, and having a thermal
value such as a thermal expansion coefficient and a value such as
ductility close to those of the adjacent semiconductor film 102 is
preferably used. Further, the cap film 103 is preferably a solid
and dense film with low etching rate similarly to a gate insulating
film of a thin film transistor to be formed later. Such a solid and
dense film can be formed by reducing a deposition rate, for
example.
When a solid and dense film is formed as the cap film 103,
appropriate loads are given to the semiconductor film 102 in
melting and solidification of the semiconductor film 102, whereby
the volume change is suppressed and stable crystal growth is
promoted. Further, irradiation with a laser beam is performed with
a power that is slightly higher than a lower limit of power density
that makes the semiconductor film 102 completely to be melted. In
such a manner, heat quantity applied to the semiconductor film 102
is reduced to necessity minimum, whereby generation of crystal
nuclei more than needs and reduction in viscosity of the melted
semiconductor film 102 are suppressed, and generation of turbulent
flow, that is, disordered crystal growth is suppressed. As a
result, orientation of crystal planes in the crystalline
semiconductor film can be easily controlled.
As described above, the semiconductor film 102 over which the cap
film 103 is formed is irradiated with a CW laser or a pseudo CW
laser under the predetermined conditions while the substrate 100 is
scanned, and crystal is laterally grown, so that a crystalline
semiconductor film 106 including large grain crystals in which
orientation of plane crystals is controlled in one direction can be
formed.
Next, as shown in FIG. 1B, by irradiating part of the semiconductor
film 102 with a laser beam 105, whereby the semiconductor film 102
is melted, so that a crystalline semiconductor film 106 in which
surface crystal planes are orientated along {001} is formed. For
example, when the power of the laser beam 105 is 8.4 W and the
scanning speed thereof is 20 cm/second, 40% or more of surfaces of
crystals planes in the crystalline semiconductor film 106 are
orientated along {001}.
The semiconductor film 102 can be irradiated with the laser beam
105 from the cap film 103 side. When the substrate 100 has a
light-transmitting property, the semiconductor film 102 can be
irradiated from the substrate 100 side. Here, the semiconductor
film 102 is irradiated with the laser beam 105 from the cap film
103 side.
The power of the laser beam 105 is preferably the low limit power
of melting the semiconductor film 102 completely or the power that
is slightly higher than the low limit power. By reducing the heat
quantity that is applied to the semiconductor film 102 to the
necessity minimum, turbulent flow of melt of the semiconductor can
be suppressed, and generation of crystal nuclei more than needs due
to turbulent flow can be suppressed. As a result, large grain
crystals can be formed.
Next, the cap film 103 over the crystalline semiconductor film 106
is removed. Typically, a mixture solution containing ammonium
hydrogen fluoride and ammonium fluoride or a hydrofluoric aqueous
solution can used for removing the cap film 103 in the case of wet
etching, and a hydrofluorocarbon gas can be used for removing the
cap film 103 in the case of dry etching.
Note that the thickness of the crystalline semiconductor film 106
may be reduced here. Typically, etching may be performed so as to
reduce the entire thickness of the crystalline semiconductor film
106 to greater than or equal to 10 nm and less than or equal to 30
nm. Furthermore, a surface of the crystalline semiconductor film
106 is coated with resist, exposure and development are performed
to form resists in desired shapes, and the crystalline
semiconductor film 106 is etched into desired shapes using the
resist as a mask. After that, the thickness of the crystalline
semiconductor film 106 with desired shape may be reduced.
Specifically, etching may be performed so that the crystalline
semiconductor film 106 with the desired shape has a thickness of
greater than or equal to 10 nm and less than or equal to 30 nm.
When a thin film transistor is formed using such a thin crystalline
semiconductor film 106, a fully depleted thin film transistor is
obtained, so that a thin film transistor with high mobility can be
manufactured.
Next, as shown in FIG. 1C, the crystalline semiconductor film 106
is selectively etched into an island shape. As an etching method of
the crystalline semiconductor film, a dry etching, a wet etching,
or the like can be used. Here, the surface of the crystalline
semiconductor film is coated with resist, and then exposure and
development are performed to form a resist mask. The crystalline
semiconductor film 106 is selectively etched by a dry etching
method with flow rate of SF.sub.6:O.sub.2 set to be 4:15 using the
formed resist mask, and thereafter, the resist mask is removed.
Then, as shown in FIG. 1D, a gate insulating film 107 is formed
over the crystalline semiconductor film 106. The gate insulating
film 107 is formed of a single layer using SiN.sub.x, SiN.sub.xOy
(x>y), SiO.sub.2, SiN.sub.xO.sub.y (x<y), or the like or a
stacked structure thereof. Here, a 40-nm-thick SiN.sub.xO.sub.y
(x<y) film is formed by a plasma CVD method. Then, a gate
electrode 108 is formed. The gate electrode 108 can be formed using
metal or a crystalline semiconductor doped with an impurity
imparting one conductivity type.
In the case of using a metal for the gate electrode 108, tungsten
(W), molybdenum (Mo), titanium (Ti), tantalum (Ta), aluminum (Al),
or the like can be used. Moreover, metal nitride obtained by
nitriding the above metal can also be used. Alternatively, a
structure in which a first layer including the metal nitride and a
second layer including the metal are stacked may be used. Also, a
paste including particles can be discharged over the gate
insulating film by a droplet discharging method, and the paste is
dried and baked to form the gate electrode 108. Further, a paste
including particles can be printed over the gate insulating film by
a printing method, and the paste is dried and baked to form the
gate electrode 108. Typical examples of the particles are: gold,
silver, copper, alloy of gold and silver, alloy of gold and copper,
alloy of silver and copper, alloy of gold, silver, and copper, or
the like.
Here, a tantalum nitride film 108a with a thickness of 30 nm and a
tungsten film 108b with a thickness of 370 nm are formed by a
sputtering method over the gate insulating film 107. After that, a
resist mask formed by photolithography is used to etch the tantalum
nitride film 108a and the tungsten film 108b selectively, and the
gate electrode 108 having a shape in which an end of the tantalum
nitride film 108a extends out farther to the outside than an end of
the tungsten film 108b is formed.
Next, an impurity element imparting n-type conductivity, for
example, is added to the crystalline semiconductor film 106 using
the gate electrode 108 as a mask, so that a drain region 109 and a
source region 110 are formed.
Further, low concentration impurity regions 111 and 112 that partly
overlap with the gate electrode 108 are formed. Furthermore, a
channel region 113 that overlaps with the gate electrode 108 is
formed.
Note that the drain region 109, the source region 110, and the low
concentration impurity regions 111 and 112 are doped with
phosphorus that is an impurity element imparting n-type
conductivity. An impurity element may be As or the like.
After that, heat treatment is performed for activating the impurity
element that is added to the semiconductor layer. Here, heat
treatment is performed in a nitrogen atmosphere at 550.degree. C.
for four hours. Through the above steps, an n-channel TFT 150 is
formed.
Next, as shown in FIG. 2A, an interlayer insulating film that
insulates the gate electrode and a wiring of the TFT 150 is formed.
Here, as the interlayer insulating film, a silicon oxide film 114,
a silicon nitride film 115, and a silicon oxide film 116 are
stacked and hydrogenated.
Then, a resist pattern is formed over the interlayer insulating
films, and the interlayer insulating films are etched using this
resist pattern as a mask, whereby contact holes that reach the
drain region 109 and the source region 110 are formed. As a result,
the drain region 109 and the source region 110 are partially
exposed.
Next, as shown in FIG. 2B, the exposed surface of the crystalline
semiconductor film is washed with hydrofluoric acid; thereafter, a
metal film 117 with a thickness of 5 to 30 nm is formed by a
sputtering method so as to entirely cover the exposed drain region
109 and the exposed source region 110. Here, the metal film 117
preferably contains Ni, Co, Pt, Pd, or Cr as its main component.
Then, heat treatment is performed. By this step, silicide reaction
is generated in portions where the drain region 109 and the source
region 110 that are a crystalline semiconductor film are contacted
to the metal film, so that silicide films 118 and 119 are
formed.
Silicide reaction depends on orientation of crystal planes in the
crystalline semiconductor film. For example, it is known that
NiSi.sub.2, CoSi.sub.2, or the like is easily grown on a surface of
a silicon film in which crystal planes are orientated along {001},
and PtSi, PdSi.sub.2, NiSi.sub.2, CoSi.sub.2, CrSi.sub.2, or the
like is easily grown on a surface of a silicon film in which
crystal planes are orientated along {111}. Accordingly, by the
reaction with the above metal film formed over the crystalline
semiconductor film in which orientation of crystal planes is
controlled in one direction, silicide films in which composition is
further uniform can be formed.
Note that in the case where a gate electrode is a crystalline
semiconductor film to which conductivity is imparted, it is
possible to form a silicide film on the gate electrode as well.
Next, the unreacted metal is removed using a known etchant.
Resistance of the source and drain regions can be sufficiently
lowered by the step of forming the silicide film. Accordingly,
activation of the n-type impurity thereafter is unnecessary.
Needless to say, heat treatment, irradiation with intense light, or
irradiation with laser light can be performed for activation of the
n-type impurity.
Then, a conductive film (for example, an Al alloy wiring) is formed
over the interlayer insulating film and the contact holes, and this
conductive film is patterned, so that a drain electrode 120 and a
source electrode 121 are formed. Through the steps, the TFT 150
(n-channel TFT) can be formed.
Note that, in this embodiment mode, an example is shown in which
after formation of the interlayer insulating films over the TFT,
the silicide films are formed using exposed portions in the drain
region 109 and the source region 110 due to the contact hole.
However, it is not limited thereto. For example, after, an impurity
ion is introduced, the gate insulating film 107 is removed using
the gate electrode as a mask, and then, a metal film is formed and
heated, whereby silicide films can be formed. Alternatively, after
the gate insulating film 107 is removed using the gate electrode as
a mask, an impurity ion is introduced, and then, a metal film is
formed and heated, so that silicide films can be formed. After
that, a TFT can be manufactured by the usual process.
The present invention is not limited to the TFT structure shown in
this embodiment mode and can be applied to TFTs having other
structures. For example, a structure in which an LDD region is
arranged by overlapping with the gate electrode with the gate
insulating film interposed therebetween, that is, a GOLD
(Gate-drain Overlapped LDD) structure, may be employed.
Although this embodiment mode is described using the n-channel TFT,
it is needless to say that a p-channel TFT can be formed using a
p-type impurity element instead of the n-type impurity element.
Although this embodiment mode gives an example of a top gate TFT,
for example, an inversely staggered TFT can be employed.
Further, although this embodiment mode shows an example in which
surface crystal planes in the crystalline semiconductor film 106
are orientated along {001}, it is not limited thereto. By adjusting
conditions of laser irradiation or the like, for example, a
crystalline semiconductor film in which surface crystal planes are
orientated along {211}, {101}, or {111} can be formed.
As described above, by irradiating the semiconductor film over
which the cap film is formed with a laser to be crystallized under
the predetermined conditions, a crystalline semiconductor film
including large grain crystals in which orientation of crystal
planes is controlled in one direction can be obtained. When the
crystalline semiconductor film is used for silicide, the random
silicide reaction that is dependent on random orientation of
crystal planes in the crystalline semiconductor film can be
suppressed, so that a uniform silicide film can be formed.
Accordingly, a semiconductor device with further little variation
can be manufactured. Thus, miniaturization and high performance of
a field effect transistor for example, can be realized.
Composition ratio, a resistance value, a thickness to be grown, and
an interface state of silicide to be formed depends on orientation
of crystal planes in a crystalline semiconductor film, and the
orientation is different depending on kinds of metal reacted with
the crystalline semiconductor film. Accordingly, in order to form a
silicide film with further high quality on the crystalline
semiconductor film, optimal orientation of crystal planes is needed
to be selected for every metal to be reacted. When an amorphous
semiconductor film over which the cap film is formed is laterally
grown using a CW laser or a pseudo CW laser, by controlling the
laser power and the scanning speed, a melting state can be
controlled. That is, by controlling the laser irradiation
condition, a crystalline semiconductor film including large grain
crystals in which orientation of crystal planes is controlled in
given orientation can be formed, so that a silicide film with
further high quality can be formed.
Since orientation of crystal planes in the crystalline
semiconductor film that can be formed can be controlled in given
orientation by control of laser irradiation conditions, an optimal
silicide film can be obtained depending on a metal used for
silicide, and a semiconductor device with high performance can be
manufactured.
Further, by forming a cap film and growing crystals laterally, a
crystalline semiconductor film whose surface is extremely flat can
be formed, so that a semiconductor device with small leak current
and high withstand voltage can be manufactured.
Embodiment Mode 2
This embodiment mode will describe a method for forming a
crystalline semiconductor film including large grain crystals in
which orientation of crystal planes is controlled in one direction
in detail, which is used in a method for forming a silicide film
described in Embodiment Mode 1.
A cap film is formed over an amorphous semiconductor film, and the
amorphous semiconductor film is irradiated through the cap film
with a continuous wave laser beam or a pulsed laser beam with
repetition rate of 10 MHz or more with the predetermined laser
power at scanning speed. As a result, a crystalline semiconductor
film including crystals in which crystal planes in the
perpendicular direction to the surface are orientated along {001},
{211}, or {101} can be manufactured. Hereinafter, a method thereof
is described with reference to drawings.
First, an optical system is described. FIG. 3 is a diagram showing
an optical system including laser oscillators that are used in
crystallization by irradiating the amorphous semiconductor film
with a laser beam for forming a beam spot.
In FIG. 3, for laser oscillators 11a and 11b, a laser oscillator
emitting a laser with a wavelength, which is absorbed in the
semiconductor film to be crystallized, by several ten % or more is
used. Typically, a second harmonic or a third harmonic can be used.
Here, a continuous laser with LD excitation (Laser Diode)
(YVO.sub.4, a second harmonic (a wavelength of 532 nm)), maximum
output of which is 20 W, is prepared. It is not necessary to
particularly limit the wavelength of the laser to a second
harmonic, but the second harmonic is superior to a further higher
other harmonic in terms of energy efficiency.
Laser power used in the present invention is within a range which
can completely melt the semiconductor film and within a range which
can form a crystalline semiconductor film with a surface in which
crystal planes are orientated along with {001}, {211}, or {101}.
When laser power that is lower than this range is used, the
semiconductor film cannot be completely melted, and a crystalline
semiconductor film in which crystal grains have small sizes and
crystal planes are not aligned in one direction is formed.
Therefore, two laser oscillators are prepared in the case of FIG.
3; however, just one laser oscillator is enough as long as the
output is sufficient. When laser power higher than this range is
used, many crystal nuclei are generated in the semiconductor film,
and from the crystal nuclei, disordered crystal growth is
generated; thus, a crystalline semiconductor film with uneven
position of crystal grains, size thereof, and orientation of
crystal planes therein is formed.
When the semiconductor film is irradiated with the continuous wave
laser, energy is continuously given to the semiconductor film;
therefore, when the semiconductor film is once brought to a melted
state, the melted state can be kept. Further, a solid-liquid
interface of the semiconductor film is moved by scanning the
semiconductor film with the continuous wave laser beam to form long
crystal grains in one direction along this moving direction. A
solid laser is used at that time because, as compared to a gas
laser or the like, its output has high stability and stable process
is expected.
Note that, without limitation to the continuous wave laser, it is
possible to use a pulsed laser with a repetition rate of 10 MHz or
more.
When a pulsed laser with a high repetition rate is used, the
semiconductor film can always be kept in the melting state through
the whole thickness, as long as a pulse interval of the laser is
shorter than time from melting to solidification of the
semiconductor film. Thus, a semiconductor film including long
crystal grains that are laterally grown in one direction by the
movement of the solid-liquid interface can be formed.
Although a YVO.sub.4 laser is used for the oscillators 11a and 11b
in this embodiment mode, other continuous wave lasers and pulsed
lasers having a repetition rate of 10 MHz or more can also be used.
For example, an Ar laser, a Kr laser, a CO.sub.2 laser, or the like
is given as a gas laser. A YAG laser, a YLF laser, a YAlO.sub.3
laser, a GdVO.sub.4 laser, a KGW laser, a KYW laser, an alexandrite
laser, a Ti: sapphire laser, a Y.sub.2O.sub.3 laser, a YVO.sub.4
laser, or the like is given as a solid laser. Moreover, there is a
ceramic laser such as a YAG laser, a Y.sub.2O.sub.3 laser, a
GdVO.sub.4 laser, or a YVO.sub.4 laser. As a metal vapor laser, a
helium cadmium laser and the like can be given.
In addition, energy uniformity of a linear beam spot that can be
obtained on the surface to be irradiated can be increased, when the
laser beam can be emitted with the laser oscillation of TEM.sub.00
(a single transverse mode) by the laser oscillators 11a and 11b,
which is preferable.
Laser beams 12a and 12b are emitted with the same energy from the
laser oscillators 11a and 11b, respectively. A polarization
direction of the laser beam 12b emitted from the laser oscillator
11b is changed through a wavelength plate 13 because the two laser
beams having polarization directions different from each other are
combined at a polarizer 14.
After the laser beam 12b passes through the wavelength plate 13,
the laser beam 12b is reflected by a mirror 22 and made to enter
the polarizer 14. Then, the laser beam 12a and the laser beam 12b
are combined at the polarizer 14 to form a laser beam 12. The
wavelength plate 13 and the polarizer 14 are adjusted so that the
beam that has been transmitted through the wavelength plate 13 and
the polarizer 14 has appropriate energy. Note that, in this
embodiment mode, the polarizer 14 is used for combining the laser
beams; however, other optical elements such as a polarization beam
splitter may also be used.
The laser beam 12 that is combined by the polarizer 14 is reflected
by a mirror 15, and the laser beam in a cross-sectional shape is
formed into a linear shape on a surface to be irradiated 18 by a
cylindrical lens 16 having a focal length of, for example, 150 mm,
and a cylindrical lens 17 having a focal length of, for example, 20
mm. The mirror 15 may be provided depending on an arrangement
condition of an optical system of a laser irradiation
apparatus.
The cylindrical lens 16 acts in a length direction of the beam spot
that is formed on the surface to be irradiated 18, whereas the
cylindrical lens 17 acts in a width direction thereof. Accordingly,
on the surface to be irradiated 18, a linear beam spot having a
length of approximately 500 .mu.m and a width of approximately 20
.mu.m, for example, is formed. Note that, in this embodiment mode,
the cylindrical lenses are used to form the beam spot into a linear
shape; however, the present invention is not limited thereto, and
other optical elements such as a spherical lens may also be used.
Moreover, the focal lengths of the cylindrical lenses are not
limited to the above values and can be appropriately set.
Although the laser beam is shaped using the cylindrical lens 16 and
17 in this embodiment mode, an optical system for stretching the
laser beam in a linear shape and an optical system for converging
thin in a surface to be irradiated may be provided independently.
For example, a cylindrical lens array, a diffractive optical
element, an optical waveguide, or the like can be used for shaping
a cross section of the laser beam in a linear shape. Alternatively,
when a laser medium in a rectangular is used, it is possible to
shape a cross section of the laser beam in a linear shape in an
emission state.
In the present invention, as described above, a ceramic laser can
be used. When the ceramic laser is used, a shape of a laser medium
can be shaped relatively freely; therefore, the ceramic laser is
suitable for forming such a laser beam. Note that the
cross-sectional shape of the laser beam that is formed into a
linear shape is preferably as narrow as possible in width, which
increases an energy density of the laser beam in the semiconductor
film; therefore, process time can be shortened.
Then, an irradiation method of the laser beam will be described.
Since the surface to be irradiated 18, where the semiconductor film
covered with the cap film is formed, is moved at a relatively high
speed, the surface to be irradiated 18 is fixed to a suction stage
19. The suction stage 19 can be moved in X and Y directions in a
plane parallel to the surface to be irradiated 18 by an X-axis
one-axis robot 20 and a Y-axis one-axis robot 21. The one-axis
robots are arranged so that the length direction of the linear beam
spot corresponds to the Y axis.
Next, the surface to be irradiated 18 is made to move along the
width direction of the beam spot, that is, along the X axis, and
the surface to be irradiated 18 is irradiated with the laser beam.
Here, a scanning speed of the X-axis one-axis robot 20 is greater
than or equal to 10 cm/sec and less than or equal to 100 cm/sec,
and the laser beam having an energy of greater than or equal to 2 W
and less than or equal to 15 W or less is emitted from each of the
two laser oscillators. The laser output after combining the laser
beams is greater than or equal to 4 W and less than or equal to 30
W. A region where the semiconductor film is completely melted is
formed by irradiation with the laser beam, and crystals are grown
in a step of solidification, so that a crystalline semiconductor
film of the present invention can be formed.
Energy distribution of the laser beams emitted from the laser
oscillators in a TEM.sub.00 mode is generally a Gaussian
distribution. Note that an optical system used in irradiation with
a laser beam can change a width of a region where crystal grains in
which orientation of crystal planes at three surfaces perpendicular
to each other are controlled are formed. For example, intensity of
the laser beam can be homogenized by using a lens array such as a
cylindrical lens array or a fly eye lens; a diffractive optical
element; an optical waveguide; or the like.
By irradiating the semiconductor film 102 with the laser beam,
intensity of which is homogenized, crystal grains in which
orientation of crystal planes perpendicular to the surface is
controlled can be formed in the regions irradiated with the laser
beam.
In this embodiment mode, a method is used, in which the
semiconductor film 102 that is the surface to be irradiated 18 is
moved using the X-axis one-axis robot 20 and the Y-axis one-axis
robot 21, but the present invention is not limited thereto, and the
surface to be irradiated is scanned with the laser beam using an
irradiation system moving method, in which the surface to be
irradiated 18 is fixed while an irradiation position with the laser
beam is moved; a surface to be irradiated moving method, in which
the irradiation position with the laser beam is fixed while the
surface to be irradiated 18 is moved; or a method in which these
two methods are combined.
Note that, as described above, the energy distribution of the beam
spot in a macro-axis direction, which is formed by the
above-described optical system, is a Gaussian distribution.
Therefore, crystals with small grain sizes (hereinafter, refer to
small grain size) are formed at places where the energy density is
low, at both ends of the beam spot. Thus, a part of the laser beam
may be cut by providing a slit or the like in front of the surface
to be irradiated 18, so that the surface to be irradiated 18 is
irradiated only with energy sufficient to form crystals at a
surface of a film in which orientation of crystal planes is
controlled. Alternatively, a pattern may be formed by forming a
metal film that reflects the laser beam, or the like over the cap
film 103, so that the laser beam reaches only a portion of the
semiconductor film, where crystals in which orientation of crystal
planes is controlled are formed.
Further, in order to utilize the laser beam emitted from the laser
oscillators 11a and 11b more efficiently, the energy in a length
direction of the beam spot may be uniformly distributed by using a
beam homogenizer such as a lens array or a diffractive optical
element. Further, the Y-axis one-axis robot 21 is moved by a
distance equal to the width of the crystalline semiconductor film
that is formed, and the X-axis one-axis robot 20 is made to be
scanned at a predetermined speed. By repeating a series of such
operations, the entire surface of the semiconductor film can be
efficiently crystallized.
Next, an experimental example is described with reference to
drawings, in which a crystalline region in which crystal planes in
a direction perpendicular to the surface (a viewing plane A) are
orientated along {001}, a crystalline region in which crystal plane
are orientated along {211}, and a crystalline region in which
crystal plane are orientated along {101} are formed using the above
optical system.
First, a sample is described. As an insulating film serving as a
base film, a SiN.sub.xO.sub.y (x>y) film with a thickness of 50
nm is formed by a plasma CVD method and then, a SiN.sub.xO.sub.y
(x<y) film with a thickness of 100 nm is formed by a plasma CVD
method over a substrate. Then, an amorphous silicon film with a
thickness of 66 nm is formed over the insulating film by a plasma
CVD method.
After the amorphous silicon film is formed, heat treatment for
extracting hydrogen from the amorphous semiconductor film is
performed, and a cap film is formed over the semiconductor film. As
the cap film, for example, a SiN.sub.xO.sub.y (x<y) film with a
thickness of 500 m is formed. As the etching rate of this film,
when the cap film is etched typically using a mixture solution
containing ammonium hydrogen fluoride and ammonium fluoride
(manufactured by Stella Chemifa Corporation, product name: LAL 500)
at 20.degree. C., the etching rate is greater than or equal to 1
nm/min and less than or equal to 150 nm/min, preferably, greater
than or equal to 10 nm/min and less than or equal to 130 nm/min,
and further preferably, greater than or equal to 10 nm/min and less
than or equal to 100 nm/min. The etching rate of etching using a
hydrofluorocarbon gas is greater than or equal to 100 nm/min and
less than or equal to 150 nm/min, and preferably greater than or
equal to 110 nm/min and less than or equal to 130 nm/min. The
SiN.sub.xO.sub.y (x<y) as the cap film is formed by a plasma CVD
method using monosilane (SiH.sub.4), ammonium (NH.sub.3), and
nitrous oxide (N.sub.2O) as a reaction gas.
Further, as the cap film, SiN.sub.xO.sub.y (x>y) with a
thickness of 400 nm may be formed by a plasma CVD method using
monosilane (SiH.sub.4) and ammonium (NH.sub.3) as a reaction
gas.
After that, the amorphous silicon film is irradiated with a
continuous wave laser beam or a pulsed laser beam with repetition
rate of 10 MHz or more through the cap film. An experimental result
at that time is shown in FIG. 4, which shows relation among the
scanning speed x (cm/sec) and power y (W) of the laser beam, and
orientation of crystal planes in the viewing plane A of a
crystalline silicon film to be formed.
In FIG. 4, a horizontal axis indicates the scanning speed of a
laser beam, and a vertical axis indicates the power of a laser
beam. In the Gaussian distribution of a laser beam at this time, a
portion where the energy distribution is uneven is removed by slit,
and an area of the beam spot is 500 .mu.m.times.20 .mu.m.
In a region 141 of FIG. 4, a crystalline semiconductor film
including large grain crystals, in which crystal planes of the
viewing plane A are orientated along {001}, can be formed.
In a region 142, the crystalline semiconductor film including large
grain crystals, in which crystal planes of the viewing plane A are
orientated along {211}, can be formed.
In a region 143, the crystalline semiconductor film including large
grain crystals, in which crystal planes of the viewing plane A are
orientated along {101}, can be formed.
In a region 144, the crystalline semiconductor film including small
grain crystal can be formed.
In a region 145, the crystalline semiconductor film is partially
evaporated.
In a region 146, the crystalline semiconductor film including large
grain crystals, in which orientation of crystal planes is random
can be formed. In such a region, since excess energy that is more
than that necessary for forming large grain crystals is supplied to
the semiconductor film, a plurality of turbulent flows are
generated, so that orientation of crystal planes is random.
In FIG. 4, the range (region 141) of power and scanning speed of
the laser beam, where crystals in which crystal planes are
orientated along {001} can be formed in the viewing plane A, is
located above the range of power and scanning speed of the laser
beam in which the crystalline semiconductor including small grain
crystals is formed; and located below the range of power and
scanning speed of the laser beam where crystals in which crystal
planes are orientated along {211} are not formed in the viewing
plane A.
In other words, at the scanning speed of the laser beam of 10
cm/sec or more and less than 20 cm/sec, the region 141 is within a
range of the scanning speed x and the power y of the laser beam
which satisfies Formula 1 or more and less than Formula 2. Formula
1 indicates a relation between power and scanning speed of the
laser beam by which crystals in which crystal planes are orientated
along {001} can be formed in the viewing plane A. Formula 2
indicates a relation between power and scanning speed of the laser
beam by which crystals in which crystal planes are orientated along
{211} are not formed in the viewing plane A. Further, at the
scanning speed of 20 cm/sec or more and less than 35 cm/sec, the
region 141 is within a range of the scanning speed x and the power
y of the laser beam which satisfies Formula 1 or more and less than
Formula 3. Formula 3 indicates a relation between power and
scanning speed of the laser beam by which crystals in which crystal
planes are orientated along {211} are not formed in the viewing
plane A. y=0.0012x.sup.2+0.083x+4.4 (Formula 1) y=0.28x+4.2
(Formula 2) y=-0.0683x+11.167 (Formula 3)
The range (region 142) of power and scanning speed of the laser
beam, where crystals in which crystal planes are orientated along
{211} can be formed in the viewing plane A, is located above the
rage of power and scanning speed of the laser beam where the
crystalline semiconductor including small grain crystals is formed;
located above the range of power and scanning speed of the laser
beam where crystals in which crystal planes are orientated along
{001} are formed in the viewing plane A; and located below the
range of power and scanning speed of the laser beam where the
crystalline semiconductor film is partially evaporated; or located
below the range of power and scanning speed of the laser beam where
the crystalline semiconductor film including large grain crystals
in which orientation of crystal planes is random is formed.
In other words, at the scanning speed of 10 cm/sec or more and less
than 20 cm/sec, the region 142 is within a range of the scanning
speed x and the power y of the laser beam which satisfies Formula 2
or more and less than Formula 4. Formula 4 indicates a relation of
power of a laser beam by which crystals in which crystal planes are
orientated along {211} can be formed in the viewing plane A.
Further, at the scanning speed of 20 cm/sec or more and less than
35 cm/sec, the region 142 is within a range of the scanning speed x
and the power y of the laser beam which satisfies Formula 3 or more
and less than Formula 4. Furthermore, at the scanning speed of 35
cm/sec or more and less than 55 cm/sec, the region 142 is within a
range of the scanning speed x and the power y of the laser beam
which satisfies Formula 1 or more and less than Formula 5. Formula
5 indicates a relation of a power of a laser beam by which crystals
in which crystal planes are orientated along {211} can be formed in
the viewing plane A. y=0.0027x.sup.2+0.36x+4.2 (Formula 4)
y=-0.37x+33 (Formula 5)
The range (region 143) of power and scanning speed of the laser
beam, where crystals in which crystal planes are orientated along
{101} can be formed in the viewing plane A, is located above the
range of power and scanning speed of the laser beam in which the
crystalline semiconductor including small grain crystals is formed;
and located below the range of power and scanning speed of the
laser beam in which the crystalline semiconductor film is partially
evaporated; or located below the range of power and scanning speed
of the laser beam where the crystalline semiconductor film
including large grain crystals in which orientation of crystal
planes is random is formed.
In other words, at the scanning speed of 70 cm/sec or more and less
than 90 cm/sec, the region 143 is within a range of Formula 1 or
more and less than the conditions where the crystalline
semiconductor film is partially evaporated, or within a range of
the scanning speed x and the power y of the laser beam where the
crystalline semiconductor film includes large grain crystals in
which orientation of crystal planes is random.
By irradiating the amorphous silicon film with the laser beam with
the above power and scanning speed selectively, a crystalline
region in which crystal planes are orientated along {001}, a
crystalline region in which crystal planes are orientated along
{211}, and a crystalline region in which crystal planes are
orientated along {101} can be selectively formed.
The crystalline region in which crystal planes are orientated along
{001} in the viewing plane A is orientation of crystal planes which
does not interfere with movement of electrons. The crystalline
region in which crystal planes are orientated along {211} or {101}
in the viewing plane A is orientation of crystal planes which does
not interfere with movement of holes. Therefore, an n-channel thin
film transistor is formed using the crystalline region in which
crystal planes are orientated along {001} in the viewing plane A,
and a p-channel thin film transistor is formed using the
crystalline region in which crystal planes are orientated along
{211} or {101} in the viewing plane A, whereby a semiconductor
device in which mobility of each thin film transistor is improved
can be manufactured.
Note that formation of the cap film makes an optical absorption
coefficient of the semiconductor film to be changed due to
interference effect of a multilayer film, and naturally, the
optical absorption coefficient is changed depending on the
thickness of the cap film. It is known that a semiconductor film in
a solid state and a semiconductor film in a melted state have
different optical absorption coefficients from each other, and the
smaller a difference between the optical absorption coefficients
is, the wider a laser power margin of lateral crystal growth
becomes. That is, in a case where an absorption coefficient is
increased suddenly at the moment of melting the semiconductor film
by irradiating the solid semiconductor film with a laser beam, the
semiconductor film becomes easy to be ablated. Accordingly, it is
needless to say that the laser power in FIG. 4 is relatively
changed depending on the thicknesses of the semiconductor film and
the cap film.
Next, orientation of crystal planes in the crystalline
semiconductor film formed in this embodiment mode is described.
This embodiment mode shows results of EBSP (Electron Back Scatter
Diffraction Pattern) measurement which represents orientation of
crystal planes in the crystalline semiconductor film after the cap
film thereover is removed by an etching step.
Orientation of crystal planes within a crystal cannot be determined
by only the orientation of crystal planes from measurement of one
viewing plane in the crystal. That is because, even if orientation
of crystal planes in one viewing plane is aligned in one direction,
orientation of crystal planes within the crystal is not considered
to be aligned in a case where orientation of crystal planes in the
other viewing planes is not aligned. Therefore, when more
information on orientation of crystal planes is obtained from at
least two planes or from many planes, higher accuracy of
orientation of crystal planes within the crystal is obtained. In
other words, when distribution of orientation of crystal planes of
all three planes is uniform in the measurement region, the crystal
can be regarded as an approximately single crystal.
FIGS. 5A to 5F show orientation of crystal planes in a crystalline
semiconductor film including large grain crystals and formed under
the laser irradiation condition of the region 141 (laser power: 8.4
W, scanning speed: 20 cm/sec). FIG. 5A shows distribution of
orientation of crystal planes in a measurement region that is
perpendicular to the surface of the crystalline semiconductor film.
FIG. 5D shows distribution of the orientation ratio of orientation
of crystal planes in the same direction with FIG. 5A, in which red
portions (portion of R in the drawing) have highest frequency, and
blue portions (portion of B in the drawing) have lowest frequency.
It is found that crystal planes in the perpendicular direction to
the surface are orientated along {001} because the portion of {001}
is red.
Similarly, FIG. 5B shows distribution of orientation of crystal
planes in a measurement region in the direction that is parallel to
the surface of the crystalline semiconductor film and that is
perpendicular to the scanning direction of a laser beam. FIG. 5E
shows distribution of orientation ratio of the orientation of
crystal planes in the same direction with FIG. 5B. FIG. 5C shows
distribution of orientation of crystal planes in a measurement
region in the direction that is parallel to the surface of the
crystalline semiconductor film and that is parallel to the scanning
direction of the laser beam, and FIG. 5F shows distribution of
orientation ratio of the orientation of crystal planes in the same
direction. From FIGS. 5B, 5C, 5E, 5F, in both of the direction that
is parallel to the surface of the crystalline semiconductor film
and that is perpendicular to the scanning direction of the laser
beam; and the direction that is parallel to the surface of the
crystalline semiconductor film and that is parallel to the scanning
direction of the laser beam, crystal planes are orientated along
{x01}. It is noticed that each measurement region is occupied by
crystals in which crystal planes are orientated in one direction at
the rate of greater than or equal to 40% and less than or equal to
100%, preferably, greater than or equal to 60% and less than or
equal to 100%.
Note that the orientation of crystal planes {x01} (x=0, 1, 2, 3)
indicates the total amount of orientation ratios of orientation of
crystal planes {001}, {301}, {201}, and {101}.
FIGS. 6A to 6F show orientation of crystal planes in a crystalline
semiconductor film including large grain crystals and formed under
the laser irradiation condition of the region 142 (laser power:
10.8 W, scanning speed: 20 cm/sec). FIG. 6A shows distribution of
orientation of crystal planes in a measurement region in
perpendicular direction to the surface of the crystalline
semiconductor film, and FIG. 6D shows distribution of orientation
ratio of orientation of crystal planes in the same direction with
FIG. 6A. Similarly, FIG. 6B shows distribution of orientation of
crystal planes in a measurement region in the direction that is
parallel to the surface of the crystalline semiconductor film and
that is perpendicular to the scanning direction of the laser beam.
FIG. 6E shows distribution of orientation ratio of orientation of
crystal planes in the same direction with the FIG. 6B. FIG. 6C
shows distribution of orientation of crystal planes in a
measurement region in the direction that is parallel to the surface
of the crystalline semiconductor film and that is parallel to the
scanning direction of the laser beam. FIG. 6F shows distribution of
orientation ratio of orientation of crystal planes in the same
direction of FIG. 6C. A way to interpret each drawing is similar to
those of FIGS. 5A to 5F.
From FIGS. 6A and 6D, it is found that in the perpendicular
direction to the surface of the crystalline semiconductor film,
crystal planes are orientated along {211}. From FIGS. 6B and 6E, it
is found that in the direction that is parallel to the surface of
the crystalline semiconductor film and that is perpendicular to the
scanning direction of the laser beam, crystal planes are orientated
along {111}. From FIGS. 6C and 6F, it is found that in the
direction that is parallel to the surface of the crystalline
semiconductor film and that is parallel to the scanning direction
of the laser beam, crystal planes are orientated along {101}. Each
measurement region is occupied by crystals in which crystal planes
are orientated in one direction at the rate of greater than or
equal to 40% and less than or equal to 100%, preferably, greater
than or equal to 60% and less than or equal to 100%.
FIGS. 7A to 7F show orientation of crystal planes in a crystalline
semiconductor film including large grain crystals and formed under
the laser irradiation condition of the region 143 (laser power: 28
W, scanning speed: 90 cm/sec). FIG. 7A shows distribution of
orientation of crystal planes in a measurement region in the
perpendicular direction to the surface of the crystalline
semiconductor film, and FIG. 7D shows distribution of the
orientation ratio of orientation of crystal planes in the same
direction. Similarly, FIG. 7B shows distribution of orientation of
crystal planes in a measurement region in the direction that is
parallel to the surface of the crystalline semiconductor film and
that is perpendicular to the scanning direction of the laser beam.
FIG. 7E shows distribution of orientation ratio of orientation of
crystal planes in the same direction with FIG. 7B. FIG. 7C shows
distribution of orientation of crystal planes in a measurement
region in the direction that is parallel to the surface of the
crystalline semiconductor film and that is parallel to the scanning
direction of the laser beam. FIG. 7F shows distribution of the
orientation ratio of orientation of crystal planes in the same
direction with FIG. 7C. A way to interpret each diagram is similar
to those of FIGS. 5A to 5F.
From FIGS. 7A and 7D, it is found that the crystal planes in the
perpendicular direction to the surface of the crystalline
semiconductor film are orientated along {101}. From FIGS. 7B and
7E, it is found that in the direction that is parallel to the
surface of the crystalline semiconductor film and that is
perpendicular to the scanning direction of the laser beam, crystal
planes are orientated along {101}. From FIGS. 7C and 7F, it is
found that in the direction that is parallel to the surface of the
crystalline semiconductor film and that is parallel to the scanning
direction of the laser beam, crystal planes are orientated along
{001}. Each measurement region is occupied by crystals in which
crystal planes are orientated in one direction at the rate of
greater than or equal to 40% and less than or equal to 100%,
preferably, greater than or equal to 60% and less than or equal to
100%.
As described above, the semiconductor film over which the cap film
is formed is irradiated with a CW laser or a pseudo CW laser, and
crystals are grown laterally, so that a crystalline semiconductor
film including large grain crystals, in which crystal planes are
orientated in one direction, can be formed.
Further, orientation of crystal planes can be controlled optionally
in the crystalline semiconductor film that can be formed by control
of the laser irradiation condition. Therefore, in a case where a
silicide film is formed, an optimal silicide film can be obtained
depending on metal used for silicide, and a semiconductor device
with high performance can be manufactured.
Furthermore, the cap film is formed and the crystals are grown
laterally, whereby a crystalline semiconductor film, of a surface
which is extremely planarized, can be formed. Therefore, by using
this crystalline semiconductor film, for example, for a channel
region and source and drain regions of a thin film transistor, a
semiconductor device with the small amount of a leak current and
high withstand voltage can be manufactured.
Embodiment Mode 3
This embodiment mode will describe a method for manufacturing a
crystalline semiconductor film in which crystal planes in the
perpendicular direction to the surface are orientated along {111}
with reference to drawings. In this embodiment mode, a cap film is
formed over an amorphous semiconductor film, and the amorphous
semiconductor film is irradiated with a continuous wave laser beam
or a pulsed laser beam with repetition rate of 10 MHz or more
through the cap film, so that the crystalline semiconductor film is
formed. A sample to be crystallized which is same as that of
Embodiment Mode 2 is used.
FIG. 8 shows an optical system for laser irradiation used in this
embodiment mode. An optical system used in this embodiment mode is
same as the optical system used in Embodiment Mode 2 except that a
beam expander 23 is inserted between the optical laser oscillator
11a and the polarizer 14 used in Embodiment Mode 2; therefore, the
explanation of the same portions is omitted.
In FIG. 8, a laser beam 12a emitted from the laser oscillator 11a
enters the beam expander 23. Although the laser beam emitted from
the beam expander is usually adjusted to be parallel light, in this
embodiment mode, the laser beam emitted from the beam expander 23
is adjusted to be emitted with a divergence angle.
A laser beam 12b emitted from the laser oscillator 11b becomes a
linear beam with a high aspect ratio on a surface to be irradiated
similar to Embodiment Mode 1 because the laser beam 12b passes
through the same optical element as the optical system of
Embodiment Mode 2. On the other hand, the laser beam 12a emitted
from the laser oscillator 11a becomes a linear beam with a low
aspect ratio on the surface to be irradiated because the laser beam
12a passes through the same optical element as the optical system
of Embodiment Mode 1 after passing trough the beam expander 23.
Energy distribution of the laser beam on the surface to be
irradiated is shown in FIGS. 9A and 9B. FIG. 9A is a diagram
showing energy distribution in the linear beam directions, and FIG.
9B is a plane view of the beam shapes. In FIGS. 9A and 9B,
reference numeral 61a denotes energy distribution on the surface to
be irradiated with the laser beam 12a emitted from the laser
oscillator 11a, and reference numeral 61b denotes energy
distribution on the surface to be irradiated with the laser beam
12b emitted from the laser oscillator 11b.
In a case where such a linear beam in which the linear beam 61b and
the linear beam 61a are combined is used for irradiation, it
becomes possible to extend time for keeping the semiconductor film
in a melted state, as compared with the case of irradiation with
only the linear beam 61b. Accordingly, a crystalline semiconductor
film can be formed, in which orientation of crystal planes is
different from that in a crystalline semiconductor film formed by
irradiation with only the linear beam 61b.
Next, orientation of crystal planes in the crystalline
semiconductor film formed in this embodiment mode is described.
This embodiment mode show results of EBSP (electron back scatter
diffraction pattern) measurement in FIGS. 10A to 10F which
represents orientation of crystal planes in a crystalline
semiconductor film after a cap film thereover is removed by an
etching step. Power of laser emitted from the laser oscillator 11a
is 10 W, and power of laser emitted from the laser oscillator 11b
is 13 W. The scanning speed is 75 cm/sec.
FIG. 10A shows distribution of orientation of crystal planes in a
measurement region in the perpendicular direction to the surface of
the crystalline semiconductor film, and FIG. 10D shows distribution
of orientation ratio of orientation of crystal planes in the same
direction. Similarly, FIG. 10B shows distribution of orientation of
crystal planes in a measurement region in the direction that is
parallel to the surface of the crystalline semiconductor film and
that is perpendicular to the scanning direction of the laser beam.
FIG. 10E shows distribution of orientation ratio of orientation of
crystal planes in the same direction with FIG. 10B. FIG. 10C shows
distribution of orientation of crystal planes in a measurement
region in the direction that is parallel to the surface of the
crystalline semiconductor film and that is parallel to the scanning
direction of the laser beam. FIG. 10F shows distribution of
orientation ratio of orientation of crystal planes in the same
direction with the FIG. 10C. A way to interpret each diagram is
similar to those of FIGS. 5A to 5F.
From FIGS. 10A and 10B, it is found that crystal planes in the
perpendicular direction to the surface of the crystalline
semiconductor film are orientated along approximately {111}. From
FIGS. 10B and 10E, it is found that in the direction that is
parallel to the surface of the crystalline semiconductor film and
that is perpendicular to the scanning direction of the laser beam,
crystal planes are orientated along {211}. From FIGS. 10C and 10F,
it is found that in the direction that is parallel to the surface
of the crystalline semiconductor film and that is parallel to the
scanning direction of the laser beam, crystal planes are orientated
along {211}. Each measurement region is occupied by crystals in
which crystal planes are orientated in one direction at the rate of
greater than or equal to 40% and less than or equal to 100%,
preferably, greater than or equal to 60% and less than or equal to
100%.
As described above, the semiconductor film over which the cap film
is formed is irradiated with a CW laser or a pseudo CW laser and
crystals are grown laterally, so that a crystalline semiconductor
film including large grain crystals, in which orientation of
crystal planes are controlled in one direction, can be formed.
Further, orientation of crystal planes can be optionally controlled
in a crystalline semiconductor film that can be formed by control
of the laser irradiation condition. Therefore, in a case where a
silicide film is formed, an optimal silicide film can be obtained
depending on metal used for silicide, and a semiconductor device
with higher performance can be manufactured.
Furthermore, the cap film is formed and crystals are grown
laterally, whereby a crystalline semiconductor film, of a surface
which is extremely planarized, can be formed. Thus, when this
crystalline semiconductor film is used, for example, for a channel
region and source and drain region of a thin film transistor, a
semiconductor device with small leak current and high withstand
voltage can be manufactured.
Embodiment 1
This embodiment will describe an example of a method for
manufacturing an active matrix substrate using the semiconductor
film of a manufacturing method which is shown in the embodiment
modes of the present invention, with reference to drawings. FIGS.
11A to 14C are process diagrams of a method for manufacturing an
active matrix substrate in this embodiment.
In FIG. 11A, a substrate 700 is made of glass such as barium
borosilicate glass or aluminoborosilicate glass typified by #7059
glass or #1737 glass manufactured by Corning, Inc. Note that the
substrate 700 may be a quartz substrate, silicon substrate, a metal
substrate, or a stainless substrate having a surface provided with
an insulating film. Furthermore, a plastic substrate which can
withstand the processing temperature of this embodiment may be
used.
Next, a base film 701 formed of an insulating film such as a
silicon oxide film, a silicon nitride film, or a silicon oxynitride
film is formed over the substrate 700. Although the base film 701
has a two-layer structure in this embodiment, the insulating film
may be a single film or have a stacked structure with two or more
layers. As a first layer of the base film 701, a silicon oxynitride
film 701a is formed to have a thickness of 10 to 200 nm
(preferably, 50 to 100 nm), using SiH.sub.a, NH.sub.3, and N.sub.2O
as reaction gases by a plasma CVD method. In this embodiment, a
silicon oxynitride film 701a with a thickness of 50 nm (composition
ratio: Si=32%, O=27%, N=24%, H=17%) is formed. Then, as a second
layer of the base film 701, a silicon oxynitride film 701b is
formed to have a thickness of 50 to 200 nm (preferably, 100 to 150
nm), using SiH.sub.4 and N.sub.2O as reaction gases by a plasma CVD
method. In this embodiment, a silicon oxynitride film 701b with a
thickness of 100 nm (composition ratio: Si=32%, O=59%, N=7%, H=2%)
is formed.
Next, a semiconductor film 702 is formed over the base film 701.
The semiconductor film 702 is formed to have an amorphous structure
with a thickness of 20 to 80 nm by a known method (such as a
sputtering method, an LPCVD method, or a plasma CVD method). A
material of the semiconductor film is not limited, and the
semiconductor film is preferably formed using silicon or a silicon
germanium (SiGe) alloy. In this embodiment, an amorphous silicon
film with a thickness of 30 nm is formed by a plasma CVD
method.
Then, a cap film 703 is formed over the semiconductor film 702. As
the cap film 703, SiON is deposited to have a thickness of 300 nm
by a plasma CVD method.
Then, as shown in FIG. 11B, the semiconductor film 702 is
crystallized to form a crystalline semiconductor film 801, and
then, the cap film 703 is removed by a method for manufacturing a
crystalline semiconductor film shown in Embodiment Modes 1 to
3.
Next, as shown in FIG. 11C, the crystalline semiconductor film 801
that is obtained by a laser crystallization method is patterned
into a desired shape, thereby forming semiconductor layers 802 to
806.
After formation of the semiconductor layers 802 to 806, doping of a
minute amount of impurity elements (boron or phosphorus) may be
performed in order to control the threshold value of TFTs.
Next, a gate insulating film 807 with which the semiconductor
layers 802 to 806 are covered is formed. The gate insulating film
807 is formed using an insulating film containing silicon with a
thickness of 40 to 150 nm by a plasma CVD method or a sputtering
method. In this embodiment, a silicon oxynitride film (composition
ratio: Si=32%, O=59%, N=7%, H=2%) with a thickness of 110 nm is
formed by a plasma CVD method. Naturally, the gate insulating film
is not limited to a silicon oxynitride film, and the gate
insulating film may be another insulating film containing silicon
of a single layer or a stacked structure.
In the case of using a silicon oxide film, TEOS (tetraethyl
Orthosilicate) and O.sub.2 are mixed by a plasma CVD method, and
discharge is performed under conditions where a reaction pressure
is 40 Pa, a substrate temperature is 300 to 400.degree. C., and a
high frequency (13.56 MHz) power density is 0.5 to 0.8 W/cm.sup.2,
so that the silicon oxide film can be formed. The silicon oxide
film manufactured in such a manner can obtain favorable
characteristics as the gate insulating film by thermal annealing of
400 to 500.degree. C. afterward.
Next, a first conductive film 808 with a thickness of 20 to 100 nm
and a second conductive film 809 with a thickness of 100 to 400 nm
are stacked over the gate insulating film 807. In this embodiment,
a first conductive film 808 formed of a tantalum nitride film with
a thickness of 30 nm and a second conductive film 809 formed of a W
film with a thickness of 370 nm are stacked. The tantalum nitride
film is formed by a sputtering method using Ta as a target in an
atmosphere containing nitrogen. The W film is formed by a
sputtering method using W as a target. Further, the W film can be
formed by a thermal CVD method using tungsten hexafluoride
(WF.sub.6). In any case, it is necessary that resistance is to be
lowered for using the first and second conductive films as a gate
electrode, and resistivity of the W film is desirably set to be 20
.mu..OMEGA. cm or less. In the W film, resistivity can be attempted
to be lowered by increasing sizes of crystal grains; however, when
the large amount of impurity elements such as oxygen are included
in the W film, the crystallization is inhibited, and resistivity is
increased. Accordingly, in this embodiment, the W film is formed by
a sputtering method using W with high purity (purity of 99.9999%)
as a target and by sufficiently considering that impurities are not
entered from a vapor phase in deposition, so that resistivity of 9
to 20 .mu..OMEGA.cm could be achieved.
Although the first conductive film 808 is tantalum nitride and the
second conductive film 809 is W in this embodiment, materials of
the first and second conductive films are not particularly limited,
and each of the conductive films may be formed using an element
selected from Ta, W, Ti, Mo, Al, Cu, Cr, or Nd, or an alloy
material or a compound material containing an element as listed
above as its main component. Further, a semiconductor film may be
used, which is typified by a crystalline silicon film doped with an
impurity element such as phosphorus. An AgPdCu alloy may be used.
Furthermore, the following combinations of films may be employed: a
combination of a tantalum (Ta) film as the first conductive film
and a W film as a second conductive film; a combination of a
titanium nitride film as the first conductive film and a W film of
the second conductive film; a combination of a titanium nitride
film as the first conductive film and a W film as the second
conductive film; a combination of a tantalum nitride film as the
first conductive film and an Al film as the second conductive film;
or a combination of a tantalum nitride film as the first conductive
film and a Cu film as the second conductive film.
Next, as shown in FIG. 11D, resist masks 810 to 815 are formed
using a photolithography method, and first etching treatment for
forming electrodes and wirings is performed. The first etching
treatment is performed under first and second etching conditions.
In this embodiment, an ICP (Inductively Coupled Plasma) etching
method is used as the first etching condition. Etching is performed
as follows: as etching gases, CF.sub.4, Cl.sub.2, and O.sub.2 with
gas flow rate of 25/25/10 (sccm), respectively, are used; and RF
(13.56 MHz) power of 500 W is supplied to a coiled electrode with
pressure of 1 Pa to generate plasma. Here, a dry etching device
using ICP manufactured by Matsushita Electric Industrial Co., Ltd.
(Model E645-square ICP) is used. RF (13.56 MHz) power of 150 W is
supplied to a substrate side (sample stage), so that a negative
self-bias voltage is applied. By this first etching condition, the
W film is etched to form the first conductive layer whose end
portion is a tapered shape.
After that, etching is performed for about 30 seconds under the
second etching condition without removing the resist masks 810 to
815, in which as the etching gases, CF.sub.4 and Cl.sub.2 with gas
flow rate of 30/30 (sccm), respectively are used, and RF (13.56
MHz) power of 500 W is supplied to a coiled electrode with pressure
of 1 Pa to generate plasma. RF (13.56 MHz) power of 20 W is
supplied to the substrate side (sample stage), and a negative
self-bias is applied. In the second etching condition in which
CF.sub.4 and Cl.sub.2 are mixed, both the W film and the tantalum
nitride film are etched to the same extent. In order to perform
etching so as not to leave residues on the gate insulating film,
etching time is preferably increased by approximately 10 to
20%.
In the first etching treatment, by forming the resist masks into
suitable shapes, end portions of the first and second conductive
layers become tapered shapes due to effect of the bias voltage
applied to the substrate side. The angle of the tapered portion is
15.degree. to 45.degree.. Thus, conductive layers 817 to 822 (first
conductive layers 817a to 822a and second conductive layers 817b to
822b) in first shapes are formed of the first conductive layer and
the second conductive layer by the first etching treatment.
Reference numeral 816 denotes a gate insulating film, and regions
which are not covered with the conductive layers 817 to 822 in
first shapes are etched by approximately 20 to 50 nm to be
thin.
Then, as shown in FIG. 12A, first doping treatment is performed
without removing the resist masks, and an impurity element
imparting n-type conductivity is added to the semiconductor layers.
The doping treatment may be conducted by an ion doping method or an
ion implanting method. An ion doping method is performed with the
dose of 1.times.10.sup.13 to 5.times.10.sup.15/cm.sup.2 at an
accelerating voltage of 60 to 100 keV. In this embodiment, the dose
is 1.5.times.10.sup.15/cm.sup.2, and the accelerating voltage is 80
keV. An element belonging to Group 15 of the periodic table,
typically, phosphorus (P) or arsenic (As) is used as the impurity
element imparting n-type conductivity, but phosphorus (P) is used
here. In this case, the conductive layers 817 to 821 in the first
shapes function as masks to the impurity element imparting n-type
conductivity, and first high concentration impurity regions 706 to
710 are formed in a self-aligned manner. In the first high
concentration impurity regions 706 to 710, the impurity element
imparting n-type conductivity is added within a concentration range
of 1.times.10.sup.20 to 1.times.10.sup.21/cm.sup.2.
Next, second etching treatment is performed without removing the
resist masks. Here, CF.sub.4, Cl.sub.2, and O.sub.2 are used as
etching gases, and the W film is etched as selected. At this time,
second conductive layers 828b to 833b are formed by the second
etching treatment. On the other hand, the first conductive layers
817a to 822a are hardly etched, so that conductive layers 828 to
833 in second shapes are formed.
After that, as shown in FIG. 12B, second doping treatment is
performed without removing the resist masks. In this case, the dose
is reduced as compared with that of the first doping treatment, and
the impurity element imparting n-type conductivity is introduced at
a high accelerating voltage of 70 to 120 keV. In this embodiment,
the dose is 1.5.times.10.sup.14/cm.sup.2, and the accelerating
voltage is 90 keV. In the second doping treatment, the conductive
layers 828 to 833 in second shapes are used as masks, and the
impurity element is introduced into the semiconductor layer below
the second conductive layers 828b to 833b, so that high
concentration impurity regions 823a to 827a and low concentration
impurity regions 823b to 827b are formed.
After the resist masks are removed, resist masks 834a and 834b are
newly formed, and third etching treatment is performed as shown in
FIG. 12C. The etching treatment is performed for about 30 seconds
as follows: SF.sub.6 and Cl.sub.2 are used as etching gases with
gas flow rate of 50/10 (sccm), respectively; and RF (13.56 MHz)
power of 500 W is supplied to a coiled electrode with a pressure of
1.3 Pa to generate plasma. RF (13.56 MHz) power of 10 W is supplied
to the substrate side (sample stage), and a negative self-bias
voltage is applied. Thus, tantalum nitride films of a p-channel TFT
and TFTs in a pixel portion (pixel TFT) are etched by the third
etching treatment, so that conductive layers 835 to 838 in third
shapes are newly formed.
As shown in FIG. 13A, after the resist masks are removed, the
conductive layers 828 and 830 in third shapes and the conductive
layers 835 to 838 in second shapes are used as masks, and the gate
insulating film 816 is removed as selected, so that insulating
films 839 to 844 are formed.
Next, as shown in FIG. 13B, resist masks 845a to 845c are newly
formed, and third doping treatment is performed. By the third
doping treatment, an impurity element imparting opposite type
conductivity to the above conductivity type is added to the
semiconductor layers that are to be activation layers of the
p-channel TFTs, so that impurity regions 846 and 847 are formed.
The second conductive layers 835a and 838a are used as masks to the
impurity element, and an impurity element imparting p-type
conductivity is added, whereby impurity regions are formed in a
self-aligned manner. In this embodiment, the impurity regions 846
and 847 are formed by an ion doping method using diborane
(B.sub.2H.sub.6) (FIG. 13B). In the third doping treatment, the
semiconductor layers included in n-channel TFTs are covered with
the masks 845a to 845c. By the first doping treatment and the
second doping treatment, the impurity regions 846 and 847 are doped
with phosphorus with different concentrations from each other.
However, the doping treatment is conducted so that each region can
have a concentration of the impurity element imparting p-type
conductivity of 2.times.10.sup.20 to 2.times.10.sup.21/cm.sup.3,
whereby there is no problem for serving the regions as a source
region and a drain region of the p-channel TFT. In this embodiment,
since the semiconductor layers to be activation layers of the
p-channel TFTs are partially exposed, there is an advantage in that
the impurity element (boron) is easily added.
Through the above steps, impurity regions are formed in each
semiconductor layer.
Next, the resist masks 845a to 845c are removed, and a first
interlayer insulating film 861 is formed. The first interlayer
insulating film 861 is formed using an insulating film containing
silicon with a thickness of 100 to 200 nm by a plasma CVD method or
a sputtering method. In this embodiment, a silicon oxynitride film
with a thickness of 150 nm is formed by a plasma CVD method. As a
matter of course, the first interlayer insulating film 861 is not
limited to the silicon oxynitride film, and may be, another
insulating film containing silicon of a single layer or a stacked
structure.
Next, as shown in FIG. 13C, by heat treatment, recovery of
crystalline of the semiconductor layers and activation of the
impurity elements added to each semiconductor layer are performed.
This heat treatment is conducted by a thermal annealing method
using an annealing furnace. A thermal annealing method may be
conducted in a nitrogen atmosphere in which the oxygen
concentration is 1 ppm or less, preferably, 0.1 ppm or less, at 400
to 700.degree. C., typically, 500 to 550.degree. C. In this
embodiment, activation of the impurity elements is performed by
heat treatment at 550.degree. C. for four hours. Other than a
thermal annealing method, a laser annealing method or a rapid
thermal annealing method (RTA method) can be applied. In the case
of a laser annealing method, a method described in the embodiment
modes of the present invention may, be employed; however, ablation
in the gate and the like may occur depending on the given energy
density, and it is necessary to pay attention to the
conditions.
Before the first interlayer insulating film 861 is formed, heat
treatment may be performed. However, in a case where an used wiring
material is weak to heat, activation treatment is preferably
performed after an interlayer insulating film (an insulating film
containing silicon as its main component, e.g., a silicon nitride
film) is formed so as to protect a wiring and the like as this
embodiment.
In addition, heat treatment is performed in an atmosphere
containing hydrogen of 3 to 100% at 300 to 550.degree. C. for 1 to
12 hours, whereby a step of hydrogenating the semiconductor layers
is performed. In this embodiment, heat treatment is performed in a
nitrogen atmosphere containing hydrogen of about 3% at 410.degree.
C. for one hour. This step is for terminating dangling bonds of the
semiconductor layers by hydrogen contained in the interlayer
insulating film. As another method of hydrogenation, plasma
hydrogenation (using hydrogen excited by plasma) may also be
performed.
In the case using a conventional laser annealing method as
activation treatment, after the above hydrogenation is performed,
the semiconductor layers are desirably irradiated with a laser beam
such as an excimer laser or a YAG laser.
Next, as shown in FIG. 14A, a second interlayer insulating film 862
is formed using an inorganic insulating material or an organic
insulating material over the first interlayer insulating film 861.
Contact holes for making contact with the electrodes are formed in
the predetermined positions in the first interlayer insulating film
861 and the second interlayer insulating film 862 (on the source
and drain regions). In this embodiment, an acrylic resin film with
a thickness of 1.6 .mu.m whose viscosity is 10 to 1000 cp,
preferably, 40 to 200 cp, and surface has a depression and
projection, is formed.
In this embodiment, in order to prevent specular reflection, the
second interlayer insulating film whose surface has a depression
and a projection is formed, whereby a depression and a projection
are formed on a surface of a pixel electrode. In order to have a
light scattering property by forming a depression and a projection
on the surface of the pixel electrode, a projection may be formed
in a region in a lower part of the pixel electrode. In that case,
the projection can be formed using the same photomask as that in
formation of the TFTs; therefore, the number of steps is not
increased. Note that this projection may be provided, as
appropriate, over the substrate in the pixel region other than the
wiring and TFT portions. Thus, a depression and a projection are
formed on the surface of the pixel electrode along with the
depression and the projection formed on the surface of the
insulating film with which the projection is covered.
Alternatively, a film for planarizing a surface may be used as the
second interlayer insulating film 862. In that case, after the
pixel electrode is formed, a depression and a projection are formed
on a surface by adding a known step such as a sandblast method, an
etching method, or the like, so that specular reflection is
prevented and reflection light is scattered, whereby whiteness
degree is preferably increased.
Next, as shown in FIG. 14B, the surface is washed with hydrofluoric
acid similarly to Embodiment Mode 1; thereafter, a metal film 871
is formed with a thickness of 5 to 30 nm so as to cover the second
high concentration impurity regions 823a to 827a exposed by a
sputtering method. Then, heat treatment is performed. The metal
film 871 here preferably contains Ni, Co, Pt, Pd, or Cr as its main
component. By this step, silicide reaction is generated in portions
where the second high concentration impurity regions 823a to 827a
in the crystalline semiconductor film and the metal film are
contacted, so that silicide films 872 to 877, and 879 to 881 are
formed.
Next, unreacted metal is removed using a known etchant. By the step
of forming the silicide film, resistivity of the source and drain
regions can be sufficiently lowered. Accordingly, activation of the
n-type impurity thereafter is unnecessary. It is needless to say
that heat treatment, irradiation with intensity light, or
irradiation with laser light can be performed for activation of the
n-type impurity.
Then, as shown in FIG. 14C, in a driver circuit 906, wirings 863 to
867 each of which is electrically connected to each impurity region
are formed. Theses wirings are formed by patterning a stacked film
of a Ti film with a thickness of 50 nm and an alloy film (an alloy
film of Al and Ti) with a thickness of 500 nm.
In a pixel portion 907, a pixel electrode 870, a gate wiring 869,
and a connection electrode 868 are formed. With this connection
electrode 868, a source wiring is electrically connected to the
pixel TFT. The gate wiring 869 is electrically connected to a gate
electrode of the pixel TFT. The pixel electrode 870 is electrically
connected to a drain region of the pixel TFT. In addition, the
pixel electrode 870 is electrically connected to the semiconductor
layer functioning as one of electrodes included in a storage
capacitor. As the pixel electrode 870, a film containing Al or Ag
as its main component or a material having superiority in
reflectivity such as a stacked film of Al or Ag is preferably
used.
In such a manner, the driver circuit 906 comprising a CMOS circuit
including an n-channel TFT 901 and a p-channel TFT 902, and an
n-channel TFT 903; and a pixel portion 907 comprising a pixel TFT
904 and a storage capacitor 905 can be formed over the same
substrate. Thus, an active matrix substrate is completed.
The n-channel TFT 901 of the driver circuit 906 has a channel
formation region 823c, the low concentration impurity region 823b
(GOLD region) overlapping with the first conductive layer 828a that
is partially included in the gate electrode, and the second high
concentration impurity region 823a functioning as a source or drain
region. This n-channel TFT 901 is connected to the p-channel TFT
902 through the electrode 866, whereby the CMOS circuit is formed.
This p-channel TFT 902 has a channel formation region 846d, the
impurity regions 846b and 846c formed outside the gate electrode,
and a high concentration impurity region 846a functioning as a
source or drain region. The n-channel TFT 903 has a channel
formation region 825c, a low concentration impurity region 825b
(GOLD region) overlapping with the first conductive layer 830a that
is partially included in the gate electrode, and a high
concentration impurity region 825a functioning as a source or drain
region.
The pixel TFT 904 of the pixel portion has a channel formation
region 826c, a low concentration impurity region 826b (LDD region)
formed outside the gate electrode, and a high concentration
impurity region 826a functioning as a source or drain region. An
impurity element imparting p-type conductivity is added to each of
semiconductor layers 847a and 847b functioning as one of electrodes
of the storage capacitor 905. The storage capacitor 905 includes
the insulating film 844 as a dielectric body, the electrode
(stacked layer of 838a and 838b), and the semiconductor layers 847a
to 847c.
In the pixel structure of this embodiment, an end portion of the
pixel electrode is arranged to overlap with the source wiring so as
not to pass light through a space between the pixel electrodes
without using black matrix.
Further, FIG. 15 shows a top view of the pixel portion of the
active matrix substrate manufactured in this embodiment. The
portions corresponding to FIGS. 11A to 14C are denoted by the same
reference numerals. A dotted line A-A' in FIG. 14C corresponds to a
cross-sectional view taken along a dotted line A-A' in FIG. 15.
Further, a dotted line B-B' in FIG. 14C corresponds to a
cross-sectional view taken along a dotted line B-B' in FIG. 15.
Embodiment 2
This embodiment will describe below steps of manufacturing a
reflective liquid crystal display device from the active matrix
substrate manufactured in Embodiment 1. FIG. 16 is used for
description.
First, after the active matrix substrate of FIG. 14C is obtained in
accordance with Embodiment 1, an alignment film 967 is formed over
the active matrix substrate of FIG. 14C, at least over the pixel
electrode 870, and rubbing treatment is performed. In this
embodiment, before the alignment film 967 is formed, a columnar
spacer 972 for keeping a substrate interval is formed in a desired
position by patterning an organic resin film such as an acrylic
resin film. Instead of a columnar spacer, a spherical spacer may be
dispersed entirely on the substrate surface.
Next, a counter substrate 969 is prepared. Then, colored layers 970
and 971 and a planarization film 973 are formed on the counter
substrate 969. The red colored layer 970 and the blue colored layer
971 overlap to form a light-shielding portion. Alternatively, the
red colored layer and a green colored layer may partially overlap
to form a light-shielding portion.
In this embodiment, a substrate shown in Embodiment 1 is used.
Accordingly, in FIG. 15 showing a top view of the pixel portion of
Embodiment 1, it is necessary to shield at least spaces between the
gate wiring 869 and the pixel electrode 870, the gate wiring 869
and the connection electrode 868, and the connection electrode 868
and the pixel electrode 870 from light. In this embodiment, each
colored layer is arranged so that light-shield portions of the
stacked colored layers overlap with the positions where light is to
be blocked, and the counter substrate is attached.
In such a manner, spaces between the pixels are shielded with the
light-shielded portions of the stacked colored layers without
forming a light-shield layer such as a black mask, whereby the
number of steps can be reduced.
Next, a counter electrode 976 formed using a transparent conductive
film on the planarization film 973 is formed at least in the pixel
portion, an alignment film 974 is formed on the entire surface of
the counter substrate, and rubbing treatment is performed.
Then, the active matrix substrate provided with the pixel portion
and the driver circuit is attached to the counter substrate with a
sealant 968. The sealant 968 contains filler. The two substrates
can be attached to have a uniform interval therebetween due to this
filler and the columnar spacer. After that, a liquid crystal
material 975 is injected between both substrates, and the
substrates are completely sealed with a sealing material (not
shown). The liquid crystal material 975 may be a known liquid
crystal material. In such a manner, a reflective liquid crystal
display device shown in FIG. 16 is completed. If needed, the active
matrix substrate or the counter substrate is cut into the desired
shape. Furthermore, a polarizing plate (not shown) is attached to
only the counter substrate. Then, an FPC is attached using a known
technique.
A liquid crystal display panel manufactured as described above can
be used for a display portion of various kinds of electronic
devices.
Embodiment 3
This embodiment will describe an example in which a light-emitting
device is manufactured by the present invention. In this
specification, the light-emitting device is a generic term for a
display panel where a light-emitting element formed over a
substrate is sealed between the substrate and a cover material, and
for a display module having the display panel equipped with an IC.
Note that the light-emitting element has a layer containing an
organic compound generating electroluminescence by applying an
electric field (light-emitting layer), an anode layer, and a
cathode layer. The luminescence in the organic compound includes
one or both of the light emission (fluorescence) when exciton
returns to the ground state from the singlet-excited state, and the
light emission (phosphorescence) when exciton returns to the ground
state from the triplet-excited state.
FIG. 17 is a cross-sectional view of the light-emitting device of
this embodiment. A switching TFT 1003 provided over a substrate
1100 in FIG. 17 is formed using the n-channel TFT 903 in FIG. 14C.
Accordingly, a structure of the switching TFT 1003 is the same as
that of the n-channel TFT 903 in FIG. 14C.
Although a double gate structure in which two channel formation
regions are formed is employed in this embodiment, a single gate
structure in which one channel formation region is formed or a
triple gate structure in which three channel formation regions are
formed may be employed.
A driver circuit provided over the substrate 1100 is formed using
the CMOS circuit of FIG. 14C. Accordingly, a structure of the
driver circuit is the same as those of the n-channel TFT 901 and
the p-channel TFT 902 in FIG. 14C. Note that the driver circuit has
a single gate structure in this embodiment, but the driver circuit
may have a double gate structure or a triple gate structure.
Wirings 1101 and 1103 each serve as a source wiring of the CMOS
circuit, and a wiring 1102 serves as a drain wiring. A wiring 1104
serves as a wiring that electrically connects a source wiring 1108
and a source region of the switching TFT. A wiring 1105 serves as a
wiring that electrically connects a drain wiring 1109 and a drain
region of the switching TFT.
A current control TFT 1004 is formed using the p-channel TFT 902 of
FIG. 14C. Accordingly, a structure of the current control TFT 1004
is the same as that of the p-channel TFT 902 in FIG. 14C. The
current control TFT has a single gate structure in this embodiment,
but the current control TFT may have a double gate structure or a
triple gate structure.
A wiring 1106 is a source wiring (corresponding to a current supply
line) of the current control TFT 1004. A wiring 1107 is an
electrode that is electrically connected to a pixel electrode 1110
when the wiring 1107 overlaps with the pixel electrode 1110.
Note that the pixel electrode 1110 functions as an anode of the
light-emitting element formed of a transparent conductive film. The
transparent conductive film can be formed using a compound of
indium oxide and tin oxide, a compound of indium oxide and zinc
oxide, zinc oxide, tin oxide, or indium oxide. Moreover, the
transparent conductive film doped with gallium may also be used.
The pixel electrode 1110 is formed over a flat interlayer
insulating film 1111 before forming those wirings. In this
embodiment, it is very important to planarize the steps due to the
TFTs using the interlayer insulating film 1111 including resin. The
light-emitting layer formed later is so thin that the emission
defect might occur due to the steps. Therefore, it is preferable to
planarize the surface before forming the pixel electrode so that
the light-emitting layer is formed on the plane as flat as
possible.
After formation of the wirings 1101 to 1107, a partition 1112 is
formed as shown in FIG. 17. The partition 1112 may be formed by
pattering an insulating film containing silicon or an organic resin
film each having a thickness of 100 to 400 nm.
Note that attention is needed to be paid for the element when the
partition 1112 is formed so that the element may not be damaged due
to static electricity because the partition 1112 is an insulating
film. In this embodiment, the resistivity is lowered by adding a
carbon particle or a metal particle in the insulating film, which
is a material for the partition 1112, so as to prevent the static
electricity. In such a case, the amount of the carbon particles or
the metal particles is adjusted so that the resistivity ranges from
1.times.10.sup.6 to 1.times.10.sup.12 .OMEGA.m (preferably from
1.times.10.sup.8 to 1.times.10.sup.10 .OMEGA.m).
A light-emitting layer 1113 is formed over the pixel electrode
1110. Although FIG. 17 shows only one pixel, each of light-emitting
layers corresponding to each color of R (red), G (green) or B
(blue) are made in this embodiment. In addition, in this
embodiment, a low-molecular organic light-emitting material is
formed by an evaporation method. Specifically, a stacked structure
is employed in which a 20-nm-thick copper phthalocyanine (CuPc)
film is formed as a hole-injecting layer, and a 70-nm-thick
tris-8-quinolinolato aluminum complex (Alq.sub.3) film is formed
thereover as the light-emitting layer. Adding the fluorescent
pigment such as quinacridone, perylene, DCM1, or the like to
Alq.sub.3 can control the emission color.
However, the above is an example of the organic light-emitting
material available as the light-emitting layer, and the material is
not limited at all to those described above. The light-emitting
layer, a charge-transporting layer, and a charge-injecting layer
may be freely combined to form the light-emitting layer (the layer
for emitting light and for moving the carrier for the light
emission). For instance, although this embodiment shows an example
in which the low-molecular organic light-emitting material is
employed for the light-emitting layer, a high-molecular organic
light-emitting material may also be employed. In addition, an
inorganic material such as silicon carbide can also be used as the
charge-transporting layer and the charge-injecting layer. These
organic light-emitting material and inorganic material may be known
materials.
Next, a cathode 1114 formed of a conductive film is provided over
the light-emitting layer 1113. In this embodiment, an alloy film of
aluminum and lithium is used as the conductive film. A known MgAg
film (an alloy film of magnesium and silver) may be used. A
conductive film made from an element belonging to Group 1 or 2 of
the periodic table or a conductive film to which the element is
added may be used as a material of the cathode 1114.
When the steps are conducted up to formation of the cathode 1114, a
light-emitting element 1115 is completed. Note that the
light-emitting element 1115 mentioned here is a diode including the
pixel electrode 1110 (anode), the light-emitting layer 1113, and
the cathode 1114.
It is effective to provide a passivation film 1116 so as to
completely cover the light-emitting element 1115. The passivation
film 1116 is formed using an insulating film including a carbon
film, a silicon nitride film, or a silicon nitride oxide film in a
single-layer structure or in a stacked structure.
Here, a film with good coverage is preferably used for the
passivation film, and it is effective to employ a carbon film,
especially a DLC (diamond-like carbon) film. Since the DLC film can
be formed at temperatures ranging from the room temperature to
100.degree. C. or less, the DLC film can be easily formed over the
light-emitting layer 1113 having low heat resistance. Moreover, the
DLC film has a high blocking effect against oxygen, and therefore,
it is possible to suppress oxidization of the light-emitting layer
1113. Therefore, using the DLC film can prevent the light-emitting
layer 1113 from being oxidized during the following sealing
step.
Moreover, a sealing material 1117 is provided over the passivation
film 1116 to paste a cover material 1118. A UV curable resin may be
used as the sealing material 1117 and it is effective to provide a
moisture absorption material or an antioxidant material inside. In
addition, in this embodiment, the cover material 1118 is a glass
substrate, a quartz substrate, or a plastic substrate (including a
plastic film), each having carbon films (preferably DLC films)
formed on opposite sides of the substrate.
Thus, the light-emitting device having the structure shown in FIG.
17 is completed. It is effective to perform continuously all the
steps after forming the partition 1112 up to forming the
passivation film 1116 in a film-forming apparatus of a
multi-chamber type (or an in-line type) without being exposed to
the air. Furthermore, it is possible to conduct the steps up to
pasting the cover material 1118 continuously without being exposed
to the air.
Thus, an n-channel TFT 1001, a p-channel TFT 1002, the switching
TFT (n-channel TFT) 1003, and the current control TFT (n-channel
TFT) 1004 are formed over the substrate 1100. The number of masks
needed in these manufacturing steps up to here is less than that
needed in manufacturing steps of a general active matrix
light-emitting device.
That is to say, the step of manufacturing a TFT is simplified to a
large degree, thereby improving the yield and reducing the
production cost.
In addition, as described with FIG. 17, the provision of the
impurity region overlapping the gate electrode with the insulating
film interposed therebetween can form the n-channel TFT that has
enough resistance against deterioration due to a hot-carrier
effect. Therefore, a light-emitting device with high reliability
can be obtained.
Although this embodiment shows only the structures of the pixel
portion and the driver circuit, another logical circuit such as a
signal division circuit, a D/A converter, an operational amplifier,
a y correction circuit, and the like can be further formed on the
same insulator according to the manufacturing steps in this
embodiment. Moreover, a memory and a microprocessor can be further
formed.
Further, a light-emitting device of this embodiment in which the
step up to sealing (or filling and sealing) for protecting the
light-emitting element has been completed will be described with
reference to FIGS. 18A and 18B. Note that the reference numerals
used in FIG. 17 are referred as needed.
FIG. 18A is a top view showing a state in which the step up to
sealing of the light-emitting element has been performed. FIG. 18B
is a cross-sectional view taken along a line A-A' in FIG. 18A. In
FIG. 18A, a reference numeral 1201 indicated by a dotted line
denotes a source driver circuit; 1206, a pixel portion; 1207, a
gate driver circuit; 1301, a cover material; 1302, a first sealant;
1303, a second sealant; and 1307, a sealing material provided in
the space surrounded by the first sealant 1302.
Note that a reference numeral 1304 denotes a wiring that transmits
a signal inputted to the source driver circuit 1201 and the gate
driver circuit 1207 and receives a video signal and a clock signal
from an FPC 1305 (flexible printed circuit) that is to be an
external input terminal. Although only the FPC is shown here, this
FPC may be provided with a print wiring board (PWB). The
light-emitting device in this specification includes not only the
light-emitting device itself but also the light-emitting device
equipped with the FPC or a PWB.
Next, a cross-sectional structure is described with reference to
FIG. 18B. The pixel portion 1206 and the gate driver circuit 1207
are formed over the substrate 1100, and the pixel portion 1206
includes a plurality of pixels including the current control TFT
1004 and the pixel electrode 1110 that is electrically connected to
the drain of the current control TFT 1004. The gate driver circuit
1207 includes the CMOS circuit (see FIG. 14C) in which the
n-channel TFT 1001 and the p-channel TFT 1002 are combined.
The pixel electrode 1110 serves as an anode of the light-emitting
element. In addition, the partition 1112 is formed at both ends of
the pixel electrode 1110. The light-emitting layer 1113 and the
cathode 1114 of the light emitting element are formed over the
pixel electrode 1110.
The cathode 1114 also serves as the wiring common to all the pixels
and is electrically connected to the FPC 1305 through the
connection wiring 1304. Further, all the elements included in the
pixel portion 1206 and the gate driver circuit 1207 are covered
with the cathode 1114 and the passivation film 1116.
Moreover, the cover material 1301 is pasted with the first sealant
1302. A spacer including a resin film may be provided in order to
keep the space between the cover material 1301 and the
light-emitting element. The inside of the first sealant 1302 is
filled with the sealing material 1307. It is preferable to employ
an epoxy resin as the first sealant 1302 and the sealing material
1307. In addition, it is desirable to employ a material which
hardly transmits moisture and oxygen to the first sealant 1302.
Further, a moisture absorption material or an antioxidant material
may be included inside the sealing material 1307.
The sealing material 1307 provided so as to cover the
light-emitting element also serves as an adhesive to paste the
cover material 1301. In addition, FRP (Fiberglass-Reinforced
Plastics), PVF (polyvinyl fluoride), polyester, or acrylic can be
employed as the material for a plastic substrate constituting a
part of the cover material 1301 in this embodiment.
After bonding the cover material 1301 with the use of the sealing
material 1307, a second sealant 1303 is provided so as to cover the
side surface (the exposed surface) of the sealing material 1307.
The second sealant 1303 can be formed using the same material as
that of the first sealant 1302.
The light-emitting element is filled and sealed with the sealant
1307 in such a structure as described, whereby the light-emitting
element can be completely shield from the outside, and a substance
promoting deterioration caused by oxidation of the light-emitting
layer due to moisture, oxygen, and the like can be prevented from
penetrating from the outside. Accordingly, a light-emitting device
with high reliability can be obtained.
Embodiment 4
This embodiment will describe a semiconductor device of the present
invention in which an active matrix display device including a TFT
circuit is incorporated, with reference to drawings.
As such a semiconductor device, a portable information terminal
(such as an electronic notebook, a mobile computer, and a cellular
phone), a video camera, a still camera, a personal computer, a
television, and the like can be given. Examples thereof are shown
in FIGS. 19A to 21D.
FIG. 19A is a cellular phone, which includes a main body 2001, an
audio output portion 2002, an audio input portion 2003, a display
device 2004, operation switches 2005, and an antenna 2006. The
present invention can be applied to the audio output portion 2002,
the audio input portion 2003, and the display device 2004 provided
with an active matrix substrate.
FIG. 19B is a video camera, which includes a main body 2101, a
display device 2102, an audio input portion 2103, operation
switches 2104, a battery 2105, and an image receiving portion 2106.
The present invention can be applied to the audio input portion
2103, the display device 2102 provided with an active matrix
substrate, and the image receiving portion 2106.
FIG. 19C is a mobile computer or a portable information terminal,
which includes a main body 2201, a camera portion 2202, an image
receiving portion 2203, an operation switch 2204, and a display
device 2205. The present invention can be applied to the image
receiving portion 2203 and the display device 2205 provided with an
active matrix substrate.
FIG. 19D is a goggle display, which includes a main body 2301, a
display device 2302, and an arm portion 2303. The present invention
can be applied to the display device 2302. Although not shown, the
present invention can be used for another signal control
circuit.
FIG. 19E is a portable book, which includes a main body 2501,
display devices 2502 and 2503, a storage medium 2504, operation
switches 2505, and an antenna 2506, and displays data stored in
mini discs (MD) or DVDs (Digital Versatile Disc) and data received
at the antenna. The display devices 2502 and 2503 are direct
view-type display devices, and the present invention can be applied
thereto.
FIG. 20A is a record player using a recording medium that records
programs (hereinafter, refer to as a recording medium), which
includes a main body 2601, a display device 2602, a speaker portion
2603, a recording medium 264, and an operation switch 2605. Note
that by using a DVD, a CD, or the like as the recording medium,
this device can be used for listening music, watching movie, games,
and the Internet. The present invention can be applied to the
display device 2602.
FIG. 20B is a television, which includes a main body 2701, a
support base 2702, and a display portion 2703. The present
invention can be applied to the display portion 2703.
FIG. 20C is a personal computer, which includes a main body 2801,
an image input portion 2802, a display device 2803, and a keyboard
2804. The present invention can be applied to the display device
2803.
FIG. 21A is a front projector, which includes a projection device
2901 and a screen 2902. The present invention can be applied to the
projection device and another signal control circuit.
FIG. 21B is a rear projector, which includes a main body 3001, a
projection device 3002, a mirror 3003, and a screen 3004. The
present invention can be applied to the projection device and
another signal control circuit.
FIG. 21C is a diagram illustrating a structural example of the
projection devices 2901 and 3002 in FIGS. 21A and 21B. The
projection devices 2901 and 3002 each include a light-source
optical system 3101, mirrors 3102 and 3104 to 3106, a dichroic
mirror 3103, a prism 3107, a liquid crystal display device 3108, a
retardation film 3109, and a projection optical system 3110. The
projection optical system 3110 is constituted by an optical system
including a projection lens. Although an example of a three-plate
mode is shown in this embodiment, the mode is not particularly
limited to this, and for example, a single-plate mode may be
employed. A practitioner may provide an optical system such as an
optical lens, a film having polarizing function, a film for
adjustment of a phase difference, or an IR film as appropriate in a
light path indicated by arrows in FIG. 21C.
FIG. 21D is a diagram illustrating a structural example of the
light-source optical system 3101 in FIG. 21C. In this embodiment,
the light-source optical system 3101 includes a reflector 3111, a
light source 3112, lens arrays 3113 and 3114, a
polarization-conversion 3115, and a condensing lens 3116. Note that
the light-source optical system shown in FIG. 21D is just an
example, and it is not particularly limited to this. For example, a
practitioner may provide an optical system such as an optical lens,
a film having polarizing function, a film for adjustment of a phase
difference, or an IR film as appropriate in the light-source
optical system.
In addition, the present invention can be applied to a
light-emitting display element. In such a manner, the present
invention can be applied in quite a wide range and can be applied
to electronic appliances of every field.
This application is based on Japanese Patent Application serial no.
2007-077217 filed with Japan Patent Office on Mar. 23, 2007, the
entire contents of which are hereby incorporated by reference.
* * * * *